Circuit board testing apparatus and method for testing a circuit board

ABSTRACT

A circuit board testing apparatus for testing continuity and/or short-circuit of wirings formed on a circuit board, includes an electromagnetic wave irradiator which irradiates first terminals of the wirings with an electromagnetic wave so that electrons are discharged from the first terminals by photoelectric effect. Discharged electrons are trapped by an electrode which is electrically biased to have a higher potential than that of the second terminals of the wirings, thereby causing an electric current to flow through the wirings via the electrode. Existence of open-circuit and/or short-circuit of the wirings is judged based on the current flowing the wirings.

BACKGROUND OF THE INVENTION

This invention relates to a circuit board testing apparatus and methodfor testing such electric state as continuity, open-circuit,short-circuit, of a number of wirings formed on a circuit board.

It should be appreciated that this invention is applicable to testing ofelectric state of wirings formed on any of a variety of circuit boardsor substrates such as printed circuit boards, flexible circuit boards,multi-layer circuit boards, glass substrates for use in liquid crystaldisplay or plasma display panels, and film carriers for use insemiconductor packages, and that the term “circuit boards” as used inthis specification may be any of these variety of boards.

Circuit boards are formed with a wiring pattern by a number of wiringsthereon. There have been proposed a number of testing apparatus to testwhether the wiring pattern has been formed as designed. Recent trend ofmaking small-sized and light-weighted electronic devices necessitatesarranging a wiring pattern in a complex manner in a small area. Thus, itis difficult to test open-circuits and short-circuits of wirings bydirect contact of probes with the circuit board. Therefore, there hasbeen proposed a contactless testing apparatus to test electric state ofa wiring pattern such as open circuit without causing direct contact ofprobes with a minute conductive pad.

For example, Japanese Patent No. 3080158 discloses this type ofapparatus which is adapted for testing an open or short-circuit of awiring formed on a circuit board. In the apparatus, specifically, anelectromagnetic wave is irradiated onto a pad connected to each wiringof a circuit pattern formed on a circuit board to thereby causedischarge of electrons from the pad owing to photoelectric effect. Theopen or short-circuit of the wiring is tested based on an electriccurrent which is caused by discharged electrons to run into a ground(GND) plane or external metallic plate capacitively coupled.

Japanese Unexamined Patent Publication No. 8-278342 discloses a printedboard testing apparatus which detects electrons discharged in a spaceowing to photoelectric effect to test continuity or open-circuit ofwirings of the printed board. Specifically, an electric charge sensorand an electromagnetic wave generator are movably provided above theprinted board with a specified gap or distance therebetween. Theelectric charge sensor and the electromagnetic wave generator arerelatively moved over the printed board to scan discharged electrons.The electric state of wirings are judged based on detected changes ofthe electric current.

The aforementioned conventional arts are suffered from the followingdrawbacks. In the conventional art, an electromagnetic wave is merelyirradiated onto a pad or wirings. Electrons which are discharged owingto photoelectric effect upon irradiation are returned to the pad andwirings, or dispersed in the space without being utilized for thetesting.

Further, discharged electrons form a spatial charge region, and lowerthe electron discharging efficiency of the photoelectric effect. Even ifelectrons are discharged instantaneously owing to photoelectric effect,accordingly, current flowing in the ground plate or external metallicplate cannot be measured with reliability. Thus, it is difficult toaccomplish stable and precise test efficiency.

In the apparatus of Japanese Unexamined Patent Publication No. 8-278342,further, the electric charge sensor and the electromagnetic wavegenerator are moved relatively to the printed board to scan dischargedelectrons, which consequently increases the size of the apparatus. Itwill be seen that in the case of producing a vacuumed space between theprinted board and the electric charge sensor and the electromagneticwave generator, a larger-sized vacuuming unit is required.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a circuit boardtesting apparatus and testing method which are free from the problemsresiding in the prior art.

It is another object of the present invention to provide a circuit boardtesting apparatus and testing method which can judge the continuityand/or short-circuit of wirings formed on a circuit board accurately andstably.

It is still another object of the present invention to provide a circuitboard testing apparatus and testing method which can assure moreefficient testing of the continuity and/or short-circuit of wiringsformed on a circuit board.

It is yet another object of the present invention to provide a circuitboard testing apparatus which is small in size and enables test ofwirings in a short time.

It is still further object of the invention to provide a circuit boardtesting apparatus and testing method that enables testing of wiringsformed on the circuit board with the test signals being derived from thecircuit board without mechanical mechanic contact at least on one sideof the circuit board.

According to an aspect of the present invention, a circuit board testingapparatus is adapted for testing continuity and/or short-circuit ofwirings formed on a circuit board. First terminals of the wirings areirradiated with an electromagnetic wave so that electrons are dischargedfrom the first terminals by photoelectric effect. Discharged electronsare trapped by an electrode which is electrically biased to have ahigher potential than that of the second terminals of the wirings,thereby causing an electric current to flow through the wirings via theelectrode. Existence of an open-circuit and/or a short-circuit in thewirings is judged based on the current flowing the wirings.

According to an embodiment of the invention, the first terminals areirradiated with the electromagnetic wave alternatively, one at a time.Also, the second terminals of the wirings are supplied with voltage oneat a time. Alternatively, a voltage may be supplied to the secondterminal of a wiring adjacent to a selected wiring of which firstterminal is irradiated by the electromagnetic wave.

For the testing of a circuit board having wirings including a pair ofterminals formed on a surface of the circuit board and an electricconductor formed on the surface of the circuit board or inside thecircuit board and connected to the pair of terminals, there may bepreferably provided a second electrode to be capacitively coupled to theelectric conductor. The continuity of the electric conductors is judgedbased on a current value when the first terminal of a target wiring isirradiated and another current value when the second terminal of thetarget wiring is irradiated.

For the testing of a circuit board including wirings having electricconductors formed on the surface or inside of the circuit board andelectrically connected to respective first and second terminals, theremay be preferably provided a second electrode to be capacitively coupledto the electric conductors. The short-circuit between wirings is judgedbased on a current value when the one of the first terminals isirradiated and another current value when another of the first terminalsis irradiated.

Alternatively, the electromagnetic wave may be collectively irradiatedonto the first terminals of the wirings. In this case, it may bepreferable to provide a power source having a first pole connected tothe electrode and a second pole connected to the second terminal of awiring selected for the test. The second terminals of the wirings otherthan the target wiring may be connected to the first pole of the powersource.

Alternatively, the second terminal of a target wiring may be connectedto the second pole of the power source by way of a current detector fordetecting a current of the target wiring while the second terminals ofthe wirings other than the target wiring are connected to the secondpole of the power source bypassing the current detector.

It may be preferable to enclose the first terminals of the wiringswithin an airtight closed space, and depressurize the closed space. Thedegree of depressurization is preferably 10⁻² atm.

A circuit board testing apparatus or method according to the presentinvention provide accuracy and efficiency in the testing of thecontinuity and/or short-circuit of wirings on a circuit board becauseelectrons discharged by photoelectric effect are captured by theelectrically biased electrode and cause an enhanced electric currentthrough the wirings connected with the electrode.

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiments/examples with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a circuit board testing apparatus inaccordance with a first embodiment of the present invention;

FIG. 2 is a block diagram showing an electric arrangement of the testingapparatus shown in FIG. 1;

FIG. 3 is a flowchart showing operations of the testing apparatus shownin FIG. 1;

FIG. 4 is a flowchart showing operations of an open circuit testing bythe testing apparatus shown in FIG. 1;

FIG. 5 is a timing chart in the open circuit test;

FIG. 6 is a flowchart showing operations for a short circuit testing bythe testing apparatus shown in FIG. 1;

FIG. 7 is a diagram showing a circuit board testing apparatus as amodification of the first embodiment;

FIG. 8 is a diagram showing a circuit board testing apparatus inaccordance with a second embodiment of the invention;

FIG. 9 is a block diagram showing an electric arrangement of the testingapparatus shown in FIG. 8;

FIG. 10 are graphs respectively showing changes of a potential at awiring, a current detected by a current detecting section, and an amountof electric charges charged at a capacitor upon irradiation of anelectromagnetic wave shown in FIG. 8;

FIG. 11 is a flowchart showing operations of the testing apparatus shownin FIG. 8;

FIG. 12 is a flowchart showing operations for a wiring test by theapparatus in accordance shown in FIG. 8;

FIG. 13 is a flowchart showing a wiring test operation by the apparatusshown in FIG. 8, altered from the operation shown in FIG. 12;

FIGS. 14A and 14B are sets of graphs each set showing changes of apotential at a wiring, a current detected by a current detectingsection, and an amount of electric charges as the integration of thecurrents detected by the current detecting section while theelectromagnetic wave is being irradiated with the irradiation isswitched from one terminal to another;

FIG. 15 is a diagram showing a circuit board testing apparatus as afirst modification of the second embodiment;

FIG. 16 is a diagram showing a circuit board testing apparatus as asecond modification of the second embodiment;

FIG. 17 is a diagram showing a circuit board testing apparatus inaccordance with a third embodiment of the invention;

FIG. 18 is a block diagram showing an electric arrangement of thetesting apparatus shown in FIG. 17;

FIG. 19 is a flowchart showing operations of the testing apparatus shownin FIG. 17;

FIG. 20 is a flowchart showing operations of an open circuit testing bythe testing apparatus shown in FIG. 17;

FIG. 21 is a diagram showing a testing apparatus as a first modificationof the third embodiment;

FIG. 22 is a diagram showing a testing apparatus as a secondmodification of the third embodiment;

FIG. 23 is a flowchart showing operations of an open/short circuittesting by the apparatus shown in FIG. 22;

FIG. 24 is a diagram showing a testing apparatus as a third modificationof the third embodiment;

FIG. 25 is a flowchart showing operations of an open/short circuit testby the apparatus shown in FIG. 24; and

FIG. 26 is a diagram showing a testing apparatus as a fourthmodification of the third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2 showing a circuit board testing apparatus inaccordance with a first embodiment of the invention, a circuit boardtesting apparatus is adapted to test a circuit board 10 on which asemiconductor chip is to be mounted according to C4 (Controlled CollapseChip Connection) package method.

As shown in FIG. 1, the circuit board 10 is formed with a number ofwirings 12, 121, 122 on a base plate 11. Each wiring 12, 121 or 122includes a pad portion 12 a, 121 a or 122 a which is formed on one orupper surface of the base plate 11 in correspondence to a pad portion towhich a semiconductor chip is connected, a ball grid portion 12 b, 121 bor 122 b which is formed on the opposite or bottom surface of the baseplate 11, and a conductive portion 12 c which extends through the baseplate 11 to electrically connect the pad portion 12 a, 121 a or 122 aand the ball grid portion 12 b, 121 b or 122 b. (For the simplicity ofexplanation, description will be made from now on with reference to thepad portion 12 a, ball grid portion 12 b and conductive portion 12 c asrepresentative of the above mentioned pads and conductors, unless it isrequired to refer to other pads and conductors for particular purpose.)

The pad portions 12 a are arranged at a small pitch to adapt to the padsconnected to semiconductor chips, whereas the ball grid portions 12 bare arranged at a larger pitch as compared with the pitch of the padportions 12 a. In this embodiment, the circuit board 10 having the aboveconstruction is referred to as a work to be tested by the apparatus.However, it is needless to say that a circuit board to be tested by theapparatus is not limited to the above mentioned type. It should be notedthat although the drawing shows only three wirings for clarification,actual circuit boards are formed with a great number of wirings on thetop and bottom surfaces or in the inside or on both of the two surfacesand the inside of the circuit board.

The apparatus is provided with a work holder 21 to carry one piece of acircuit board as a work 10. The work holder 21 is movable between a testposition (position shown in FIG. 1) where the work 10 is tested and aload/unload position (not shown) where the work 10 is loadable to thework holder 21 or unloadable from the work holder 21. A work drivingmechanism 22 drivingly reciprocates the work holder 21 back and forthbetween the test position and the load/unload position in accordancewith a control signal from a controller 30 which controls an overalloperation of the apparatus.

A lower fixture unit 40 is provided below the work 10 at the testposition. The lower fixture unit 40 includes a plurality of conductivespring probes 41 which are arranged in correspondence to the ball gridportions 12 b of the respective wirings 12. The lower fixture unit 40further include a multiplexer 42, and a lower fixture base (not shown)which is movable toward and away from the work 10 while carrying theprobes 41 and the multiplexer 42 thereon. The lower fixture base iscoupled to a lower fixture unit driving mechanism 43. The lower fixtureunit driving mechanism 43 drivingly moves the lower fixture, base towardand away from the work 10 in response to a control signal from thecontroller 30.

An upper fixture unit 50 is provided above the work 10 at the testposition. The upper fixture unit 50 includes a cap-like housing which isso configured as to cover a certain region on one surface of the work10. The housing includes a plate electrode 51 made of a transparentelectrode and shielding members 52 made of, e.g., a rubber. The upperfixture unit 50 is movable toward and away from the work 10 as anintegral unit. With this arrangement, when an upper fixture unit drivingmechanism 55 coupled to the upper fixture unit 50 is actuated inresponse to a drive command from the controller 30, the upper fixtureunit 50 is moved to the work 10. When an end portion 52 a of theshielding members 52 come into contact with the surface of the work 10the shielding member deforms and abuts against the surface of the work10 due to counter pressure. The end portion 52 a serves to make airtightthe enclosure surrounded by the housing 50 and the work 10. In thisembodiment, the end portion 52 a of the shielding member 52 itself isdeformable for the sealing of the enclosure. However, this invention isnot limited to this arrangement. A seal member may be provided betweenthe shielding member 52 and the work 10 as the case may be. Anatmosphere controller 70 is operatively connected to the housing 50 todepressurize the closed space SP. When the work is tested, the closedspace SP is preferably held at a vacuum degree of 10⁻² atm. In the caseof a vacuum degree lower than 10⁻² atm, the electron discharge ratedecreases, On the other hand, higher vacuum degree increases theelectron discharge rate. However, a longer time is required until theclosed space SP reaches a desired higher vacuum degree, consequentlyincreasing the test time. According to experiments of the inventors, itwas confirmed that sufficient photo-electrons are discharged under thepressure of 10⁻² atm which can be attained in a relatively short time.

The housing 50 may preferably have such a size as to cover the region onthe work 10 within which the pad portions 12 a of the wiring to betested are located. With this arrangement, the closed space SP whichneeds depressurization can be minimized. As a result, the apparatus as awhole can be made small, and the time required for depressurization canbe shortened.

An electromagnetic wave irradiator 60 is provided in the apparatus toirradiate an electromagnetic wave onto one terminal or pad of the wiringunder test, i.e. selected one of a number of wirings 12 formed on thework 12. The electromagnetic wave irradiator 60 includes anelectromagnetic wave emitting section 61 which emits an electromagneticwave L in response to an operation command from the controller 30. Anelectromagnetic wave scanning section 62 directs the electromagneticwave L to a desired location on the work 10 in response to an operationcommand from the controller 30. According to the present embodiment,electromagnetic wave emitting section 61 is constructed so as to emitultraviolet laser light beams having a wavelength of 266 nm. Also, theelectromagnetic wave emitting section 61 is provided with an opticalsystem to focus the laser light beams on the pad portion 12 a of atarget wiring 12.

In this embodiment, the electromagnetic wave emitting section 61 emitsultraviolet laser light beams for the purpose of causing thephotoelectric effect. However, this invention is not limited to thearrangement of the embodiment, and visible light beams, infrared lightbeams or its equivalent may be used.

It is generally known that the photoelectric effect comes into beingunder the following condition:

Photon Energy≧Work Function Specific to Material:Energy for DischargingElectron from Material.

Thus, light energy should be given to the material to satisfy the abovementioned inequality.

The electromagnetic wave emitting section 61 is so constructed as to bedriven based on a pulse signal with use of a Q switching element and thelike. The electromagnetic wave scanning section 62 includes agalvanometer for the control of the direction of the electromagneticwave.

A direct current (DC) power source 80 is provided in the apparatus toapply a potential difference or a voltage between the plate electrode 51and the ball grid 12 b as the opposite terminal of the wiring undertest. According to the present embodiment, the application of a voltagein the above manner enhances capturing of the electron by the electrode51 and enables efficient testing of the wiring by means of photoelectroncaused by projection of the electromagnetic wave such as a laser beamwhile suppressing return and dispersion of discharged electrons andformation of a spatial space of electric charges as well as was seen inthe prior arts.

Further, a current detecting section 90 is provided in a conductivecircuit pathway through which a current runs from one terminal of thepower source 80 to the opposite terminal thereof via the plate electrode51 and the target wiring to detect the current running in the circuitpathway. Specifically, the plus terminal of the power source 80 iselectrically connected to the plate electrode 51. The minus terminal ofthe power source 80 is connected to one terminal of the multiplexer 42via the current detecting section 90, while the opposite terminal of themultiplexer 42 is connected to a number of probes 41 which are incontact with respective corresponding ball grid portions 12 b of thewirings 12.

In this embodiment, when one wiring is selected from the number ofwirings 12 by switching over switch portions constituting themultiplexer 42 in response to a selection command from the controller 30with an output voltage from the power source 80 being applied betweenthe ball grid portion 12 b of the wiring under test and the plateelectrode 51.

Subsequently, the electromagnetic wave irradiator 60 irradiates anelectromagnetic wave L which, in turn, is projected onto the pad portion12 a of the target wiring, to thereby discharge electrons from thesurface of the pad portion 12 a due to photoelectric effect. Thedischarged electrons are electrically attracted by the plate electrode51 aided by the voltage applied thereto. This arrangement eliminates alikelihood that electrons discharged once may be returned to the padportion or dispersed to the other pad portion(s), or form a spatialregion of electric charges, as occurred in the conventional arrangement.

In this embodiment, electrons are discharged from the surface of the padportion 12 a which is connected to the ball grid portion 12 b.Accordingly, when the wiring under test is continuous and has noopen-circuit portion, a conductive circuit pathway is established fromthe plus terminal of the power source 80 to the minus terminal of thepower source 80 via the plate electrode 51, the target wiring 12, theprobe 41, the multiplexer 42, and the current detecting section 90. Thecurrent detecting section 90 measures a current running in the pathway,and outputs an analog signal corresponding to the measured current.Thus, in this embodiment, the plate electrode 51 serves as an electrodeportion, and the current detecting section 90 serves as a currentdetector.

In the embodiment mentioned above with reference to FIG. 1, one 42 a ofa number of switch portions constituting the multiplexer 42 is connectedto the opposite terminal of the power source 80, a voltage is applied tothe probe 41 a connected to the switch portion 42 a, and anelectromagnetic wave L is projected onto a pad portion 121 a connectedto the probe 41 a. In this case, a wiring 121 is a target wiring orwiring under test. If the wiring 121 is in a normal continuous state, acertain value of a current runs through the aforementioned conductivecircuit pathway due to the electrons discharged from the surface of thepad portion 121 a. On the other hand, if the wiring 121 is in adiscontinuity or open-circuited, a current value detected by the currentdetecting section 90 is zero or exceedingly lower than a current valuedetected in the case where the wiring 121 is in continuity. Thisarrangement enables the controller 30 to determine whether the targetwiring 121 is in continuity or in discontinuity based on the currentdetected by the current detecting section 90. Thus, in this embodiment,the controller 30 has a function of determining the state of the testedwiring as well as other various operation control function.

When an open circuit test with respect to the target wiring 121 iscompleted, and the connection of the switch portions is switched over toanother probe. When a new target wiring is selected by the switchportions and an electromagnetic wave is projected onto a pad portion ofthe new target wiring, an open circuit test of the new target wiring isperformed in the same manner as mentioned above. Thus, in thisembodiment, the multiplexer 42 serves as a selector.

In this embodiment, the switch connection by the multiplex 42 andselective irradiation of the pad portion also enables testing ofshort-circuit between a pair of wirings. Here, description is made for acase where the wiring 12 provided on the left side of the work 10 inFIG. 1 is referred to as “first target wiring”, and the wiring 121provided substantially transversely in the middle of the work 10 isreferred to as “second target wiring”, and a test is performed as towhether there is a short-circuited portion between the wiring pair 12and 121. In this case, for example, a middle switch portion 42 a whichis electrically connected to the second target wiring 121 is connectedto the opposite terminal of the power source 80. An electromagnetic waveL is irradiated onto the pad portion 12 a of the first target wiring 12.

Under the above mentioned condition, an electric field is generatedbetween the plate electrode 51 and the pad portion 12 a (one end) of thefirst target wiring 12 by application of a voltage to the plateelectrode 51 and the second target wiring 121. Electrons discharged bythe irradiation of the laser beam, from the pad portion 12 a of thefirst target wiring 12 are electrically attracted by the plate electrode51. In the case where a short-circuited portion exists between the firsttarget wiring 12 and the second target wiring 121, a conductive pathwayis established through which a current runs from the power source 80 andreturns thereto via the plate electrode 51, the first target wiring 12,the short-circuited portion, and the second target wiring 121. Thus, acurrent running through the target wiring pair 12 and 121 is measured bythe current detecting section 90.

On the other hand, in the case where the target wiring pair 12 and 121is not in a short circuit state, the aforementioned conductive pathwayis not established, and the current value detected by the currentdetecting section 90 is zero or exceedingly lower than the current valuedetected when the target wiring pair 12 and 121 is in a short circuitstate. This arrangement for the detection of a current running in thetarget wiring pair enables efficient and stable determination whetherthe target wiring pair is in a short circuit state or not. Test can beperformed with respect to the other wiring pairs in the similar manneras mentioned above. For instance, when the pad portion of the wiringlocated on the right side of the work 10 in FIG. 1 is irradiated with anelectromagnetic wave L in the state shown in FIG. 1, determination ismade whether there is a short-circuited portion between the secondtarget wiring 121 and the right-side wiring.

FIG. 3 is a flowchart showing an operation of the circuit board testingapparatus shown in FIG. 1. First, an untested work (circuit board) 10 isloaded onto the work holder 21 at the load/unload position by a handlingdevice (not shown) provided in the testing apparatus or a manualoperation by an operator (in Step S1). Then, the controller 30 starts tocontrol operations of the various parts of the apparatus to execute thefollowing steps S2 to S9 so as to test shorts and open-circuits in thework 10.

First, at Step S2, the work holder 21 clamps the work 10. The workholder 21 holding the work 10 thereon is moved to the test position(position shown in FIG. 1) where the work 10 is to be tested (Step S3).Thus, the work 10 is positioned at the test position.

Subsequently, the upper fixture unit 50 and the lower fixture unit 40are moved to the work 10 to pressingly hold the work 10 therebetween (inStep S4). As shown in FIG. 1, when the lower fixture unit 40 is moved tothe work 10 at the test position, a lead end of each of the conductivespring probes 41 is brought into pressing contact with the correspondingball grid portion 12 b of the wiring 12 to thereby electrically connectthe work 10 to the lower fixture unit 40. Simultaneously, as the upperfixture unit 50 is moved to the work 10 at the test position, thehousing 51 and the work 11 form an airtight closed space SP as shown inFIG. 1.

Thus, when the apparatus is set up for testing the work 10, an opencircuit test (Step S5) and a short circuit test (Step S6) areimplemented to test a continuity of the wirings of the work 10. Thesetests will be described in detail later.

Upon completion of the tests, the lower fixture unit 40 and the upperfixture unit 50 are moved away from the work 10 to release the work 10from the fixtures (in Step S7). The work holder 21 is moved to theload/unload position to release clamping of the work 10 (in Step S8). Ata final stage, upon verifying that the work 10 after the tests has beenunloaded from the work holder 21 in Step S9, the routine returns to StepS1 to execute the aforementioned series of operations with another work.

Next, the open circuit test (Step S5) is described in detail withreference to FIGS. 4 and 5. FIG. 4 is a flowchart showing an opencircuit test to be implemented by the apparatus. FIG. 5 is a timingchart for the open circuit test.

The closed space SP secured in Step S4 is filled with air containingoxygen. If an electromagnetic wave is irradiated onto the pad portion 12a in the closed space SP in this state, it is highly likely thatmolecules in the air obstruct electrons generated by photoelectriceffect from being properly discharged from the surface of the padportion, which makes it difficult to stably measure a current due to theelectrons. To avoid such a drawback, in this embodiment, the atmospherecontroller 70 is activated to depressurize the interior of the housing50 to approximately 10⁻² atm in response to an operation command fromthe controller 30 (in Step S51).

Upon completion of depressurization, as shown in FIG. 5, the multiplexer42 is activated in accordance with a selection command from thecontroller 30, and one wiring 12 (target wiring) is electricallyconnected to the minus output terminal of the power source 80 (in StepS53). Thus, the first target wiring is selected with the voltage of thepower source 80 being applied between the electrode 51 and the ball gridof the selected wiring. Then, ultraviolet laser light in the form ofpulses or another type of electromagnetic wave is irradiated onto thepad portion 12 a of the selected wiring at a predetermined timing shownin FIG. 5 (in Step 554).

During irradiation, the current detecting section 90 measures thecurrent which changes as shown in FIG. 5 (in Step S55). It is judgedwhether the target wiring is in an open circuit state or not based onthe measured current value (in Step 556). A judgment regarding an opencircuit can be performed merely based on presence or absence of adetected output. Preferably, however, an open circuit may be judged bycomparison of a current value measured with a reference circuit board,with a current measured with the circuit board under test. A series ofoperations from selection of the target wiring (Step S53) to judgmentregarding open circuit (Step S56) are repeated until it is judged thatall the wirings have been tested in Step S57.

As mentioned above, in the testing apparatus in accordance with thefirst embodiment, an electric field is generated between the plateelectrode 51 and the pad portion 121 a by application of a voltage tothe plate electrode 51 and the ball grid portion (opposite terminal) 121b of the target wiring 121. Electrons which have been discharged fromone terminal of the target wiring 121 by photoelectric effect due toelectromagnetic wave irradiation are electrically attracted by the plateelectrode 51 aided by the existence of the electric field. With thisarrangement, in the case where the target wiring 121 is in continuity, aconductive pathway is established through which a current runs from thepower source 80 and returns thereto via the plate electrode 51 and thetarget wiring 121, and a current running through the target wiring 121can be stably measured by the current detector.

On the other hand, in the case where the target wiring 121 is indiscontinuity, the aforementioned conductive pathway is not established,and the current value detected by the current detecting section 90 iszero or exceedingly lower than the current value detected in the casewhere the target wiring 121 is in continuity. In this arrangement, therecan be determined precisely and stably whether the target wiring 121 isin continuity by detecting a current running through the target wiring121.

In this embodiment, the closed space SP enclosing the pad portion to beirradiated is depressurized, and molecules in the air inside the closedspace SP which are liable to hinder discharge of electrons generated byphotoelectric effect can be reduced. Thereby, electrons are efficientlydischarged, and a stable current measurement is enabled. Further, sincethe housing 50 defining the closed space SP is so configured as to covera minimal area on the work 10, the space for depressurization can beminimized, which contributes to production of a small-sized apparatusand shortening of a time required for depressurization.

In this embodiment, a conductive pathway through which a current runsfrom the plus terminal of the power source 80 to the minus terminal ofthe power source 80 via the plate electrode 51, the target wiring 12,the probe 41, the multiplexer 42, and the current detecting section 90is established, and a judgment as to whether the target wiring is in anopen circuit state is made by measuring a change of current runningthrough the conductive pathway. In other words, since the testingapparatus is so constructed as to establish a conductive circuitpathway, a current value can be measured stably.

Further, in this embodiment, a transparent electrode is used as theplate electrode 51. This arrangement is advantageous in the followingpoint. An electromagnetic wave can be irradiated onto the pad portion ofthe target wiring even if the plate electrode 51 is provided high abovethe target wiring because the electromagnetic wave passes through thetransparent electrode 51 and is irradiated onto the pad portion. In viewof the above, in this embodiment, the plate electrode 51 can be disposedcloser to the pad portion 121 a of the target wiring 121, and electronsdischarged from the pad portion 121 a upon irradiation can be securelytrapped by the plate electrode 51 to thereby secure a more stable test.

Furthermore, in this embodiment, since the plate electrode 51 has such ashape as to cover a group of wirings to be tested, the following effectscan be obtained. Specifically, this arrangement does not need totransversely move the plate electrode 51 to match with the location ofthe target wiring, and allows an electromagnetic wave to pass throughthe plate electrode 51 and irradiate onto the target wiring while fixingthe plate electrode 51. This arrangement enables one to simplify theconstruction of the upper fixture unit 50 and the upper fixture unitdriving mechanism 55 and shorten a test time. Further, since the plateelectrode 51 constitutes a portion of the housing 50, the number ofparts constituting the apparatus can be lessened.

Next, the short circuit test (Step S6) is described with reference toFIG. 6. FIG. 6 is a flowchart showing a short circuit test by theapparatus. An overall flow of the short circuit test is basically thesame as the open circuit test (Step S5) except that the short circuittest includes switch-over control of the multiplexer 42 in associationwith irradiation onto the pad portion. Hereinafter, merely thedifferences between the short circuit test and the open circuit test aredescribed primarily focusing on the short circuit test.

Similar to the open circuit test, in the short circuit test, afterdepressurization is performed (in Step S61), a pair of target wiringsare selected in accordance with a selection command from the controller30 (in Step S63) with a voltage being applied between the electrode 51and one of the selected wiring (in Step S62). At this time, themultiplexer 42 is activated in response to a selection command from thecontroller 30 in such a manner that the minus output terminal of thepower source 80 is not electrically connected to the first target wiringconstituting the target wiring pair but is connected to the secondtarget wiring constituting the target wiring pair. On the other hand,the scanner 62 is controlled to direct the laser light beam to the pador end terminal of the first target wiring.

After the target wiring pair is selected in Step S63, an electromagneticwave is irradiated onto the pad portion of the first target wiring inresponse to an operation command from the controller 30 (in Step S64).Thereupon, electrons are discharged from the pad portion, and anelectric field is generated between the plate electrode 51 and the padportion (one terminal) of the first target wiring by application of avoltage to the plate electrode 51 and the second target wiring if thetarget wiring pair is in a short circuit state. As a result, theelectrons discharged from the first target wiring due to photoelectriceffect by electromagnetic wave irradiation are electrically attracted bythe plate electrode 51 aided by the existence of the electric field, anda conductive pathway is established through which a current runs fromthe power source 80 and returns thereto via the plate electrode 51, thefirst target wiring, the short-circuited portion, and the second targetwiring to thereby securely measure a current running through the targetwiring pair.

On the other hand, in the case where the target wiring pair is not in ashort circuit state, the aforementioned conductive pathway is notestablished, and a current value detected by the current detectingsection 90 is zero or exceedingly lower than a current value detected inthe case where the target wiring pair is in a short circuit state. Thus,this arrangement enables one to precisely and stably determine whetherthe target wiring pair is in a short circuit state by detecting acurrent running through the target wiring pair.

In this embodiment, during irradiation, the current detecting section 90measures a current and outputs a signal corresponding to the current asa detected output (in Step S65). It is judged whether the target wiringpair is in a short circuit state based on the measured current value (inStep S66). A judgment regarding short circuit can be performed simplybased on presence or absence of a detected output. Preferably, however,it is judged whether the target wiring pair is in a short circuit stateby comparing a current value measured with a reference circuit boardwith a current value measured with the circuit board under test. Aseries of operations from selection of the target wiring pair (Step S63)to judgment regarding short circuit (Step S66) are repeated until it isjudged that all the wirings on the work 10 has been tested in Step S67.

In the above mentioned first embodiment, a transparent electrode is usedas the plate electrode 51. This invention is not limited to thatarrangement. Alternatively, a mesh electrode may be provided in place ofthe plate electrode. In the altered arrangement, it is preferable that ahousing is made of a transparent glass material or the like and a meshelectrode is attached on an inner surface of the housing. En such analtered arrangement, an electromagnetic wave L passes through thehousing and clearances between the mesh electrodes to be irradiated ontoa target wiring. This altered arrangement enables one to obtain asimilar effect as the first embodiment.

Further, it would be appreciated to provide an electrode on the side ofa housing defining a closed space SP instead of the provision of anelectrode in a top of the housing. Specifically, a side wall of thehousing may be made of conductive metallic material to function asshield and electrode while a top of the housing is made of transparentglass. This construction makes connection of the electrode with anexternal power source easier.

Next, a modification of the first embodiment is described. FIG. 7 is adiagram showing the modified circuit board testing apparatus. The basicprinciple of the modified apparatus is similar to that of the apparatusin accordance with the first embodiment. The modification differs fromthe first embodiment in the manner of applying a voltage from a powersource and in the arrangement in association therewith. In view of this,constituent elements in the modification which are identical to those inthe first embodiment are denoted by the same reference numerals, and themodification is described primarily focusing on the difference of themodification from the first embodiment.

The modified apparatus is not provided with a plate electrode forapplying a voltage. In the modified apparatus, a voltage is applied toall or part of the wirings arranged in the vicinity of a target wiringsuch that the wirings may efficiently capture the electrons dischargedfrom the target wiring upon irradiation of an electromagnetic wave. Toprovide this arrangement, in the modification, the plus terminal of apower source 80 is connected to one terminal of a multiplexer 45,whereas the minus terminal of the power source 80 is connected to theopposite terminal of the multiplexer 45 via a current detecting section90.

An upper fixture unit includes a housing 54 having the shape of a cap tocover a certain area on one surface of a work 10. An optical window isformed in the housing 54 at a position above a target wiring. Theoptical window constitutes an irradiation path for guiding anelectromagnetic wave L.

More specifically, the optical window may be formed through which anelectromagnetic wave L is irradiated, or the entirety of the housing 54is made of a glass which is optically transparent or its equivalent. Thehousing 54 constituting the upper fixture unit is movable toward andaway from the work 10. An upper fixture unit driving mechanism 55 isactivated in response to a drive command from a controller 30. Thehousing 54 is moved to the work 10 until its bottom edge 54 a of thehousing 54 comes into contact with a surface of the work. Then, the endportion or bottom edge 54 a is deformed and pressed against the surfaceof the work due to counter pressure. The end portion 52 a serves as atight closure or seal. In this way, an airtight closed space SP isdefined by the work 10 and the housing 54.

Described is a case, as shown in FIG. 7 for example, in which a switchportion 45 a is connected to a terminal a, and switch portions 45 b and45 c which are remaining switch portions of the multiplexer 45 areconnected to a terminal b. In this case, a wiring 121 connected to theswitch portion 45 a is a target wiring. A certain level of voltage isapplied to wirings connected to the switch portions 45 b, 45 c from thepower source 80, and an electromagnetic wave L is irradiated onto a padportion 121 a.

In the case where the wiring 121 is in a normal continuous state, anelectric field is generated between pad portions 12 a of the wiringsconnected to the switch portions 45 b, 45 c (hereinafter, referred to as“the other wirings”) and the pad portion 121 a of the target wiring 121by applying a voltage to the opposite terminal of the target wiring 121and the other wirings. Electrons which have been discharged from the padportion 121 a of the target wiring 121 by photoelectric effect due toelectromagnetic wave irradiation are electrically attracted by the padportions 12 a.

At this time, in the case where the target wiring 121 is in continuity,a conductive pathway is established along which a current runs from thepower source 80 and returns thereto via the other wirings and the targetwiring 121 to thereby cause a current running through the target wiring121, with the current being measured by the current detecting section90.

On the other hand, in the case where the target wiring 121 is indiscontinuity, the aforementioned conductive pathway is not established,and a current value detected by the current detecting section 90 is zeroor exceedingly lower than a current value detected in the case where thewiring 121 is in continuity. This arrangement enables one to preciselyand stably determine whether the target wiring is in continuity bydetecting a current running through the target wiring 121, and enablesthe controller 30 to determine whether the target wiring 121 is incontinuity or in discontinuity based on a measured current detected bythe current detecting section 90.

When an open circuit test with respect to the target wiring 121 iscompleted, and the connecting state of the switch portions is switchedover, a new target wiring is selected one after another. After the newtarget wiring is selected by switching over the switch portions, and anelectromagnetic wave is irradiated onto a pad portion of the new targetwiring, an open circuit test with respect to the new target wiring canbe performed in the same manner as mentioned above. Thus, the opencircuit test can be performed with respect to all the wirings of thework 10.

In the modification of the first embodiment, it is required to perform ashort circuit test with respect to respective pairs of ball gridportions prior to an open circuit test when the open circuit test is tobe performed with use of the modified apparatus. This is because in thecase where there is a short-circuited portion between a pair of ballgrid portions, it is highly likely that a current may erroneously runwhen the switch portions of the multiplexer are about to be switchedover. Such short circuit testing may be made, for example, by connectingone terminal of the power source to one of the wiring and the otherterminal of the power source to another wiring through a currentmeasuring device, without the above mentioned irradiation ofelectromagnetic wave.

As mentioned above, in the modification, the pad portions 12 a of theother wirings serve as the plate electrode in the first embodiment byselectively switching over the switch portions of the multiplexer 45.While generating an electric field between the pad portion 121 a of thetarget wiring 121 and the pad portion(s) 12 a of the other wiring(s),electrons generated from the pad portion 121 a due to photoelectriceffect by electromagnetic wave irradiation are trapped by the padportion 121 a. With the arrangement of this modification,continuity/discontinuity of the target wiring can be stably determinedin the similar manner as in the first embodiment despite the fact that aplate electrode is not provided in the modification.

This invention is not limited to the aforementioned first embodiment andthe modification thereof. For instance, in the apparatus in accordancewith the first embodiment (or the modification), an open circuit testand a short circuit test are performed in this order to determinewhether a work (circuit board) 10 is in continuity. The order of testingis not limited to the above. Further, this invention is applicable toany apparatus as far as the apparatus is capable of performing at leastan open circuit test.

In the first embodiment and the modification thereof, the circuit board10 capable of mounting a semiconductor chip according to C4 packagemethod is used as a work to be tested. Alternatively, this invention isapplicable to test a circuit board in which one surface of a base plateis formed with wirings or a circuit board formed with a cuffed wiringpattern.

In the first embodiment and the modification, an electromagnetic wave Lis irradiated in the form of a pulse for one time. The number of timesof irradiation is not limited to one, and the irradiation may beperformed for a certain number of times. Further, in the firstembodiment and the modification, depressurization of the interior of ahousing is performed. Alternatively, as the case may be,depressurization may be omitted, or vacuum degree may be varieddepending on performance of the electromagnetic wave irradiator.

As mentioned above, according to the first embodiment and themodification, an electric field is generated between an electrodeportion and one terminal of a target wiring, and a conductive pathway isestablished by attracting electrons discharged from the one terminal ofthe target wiring by photoelectric effect due to electromagnetic waveirradiation onto the electrode portion aided by the existence of theelectric field. Thereby, short and open-circuit of the target wiring canbe accurately and stably tested.

FIG. 8 is a schematic illustration of a circuit board testing apparatusaccording to a second embodiment of the invention. FIG. 9 is a blockdiagram showing an electric configuration of the testing apparatus inFIG. 8. A circuit board testing apparatus in accordance with a secondembodiment is adapted to test a circuit board 210. As shown in FIG. 8,the circuit board 210 is constructed in such a manner that a number ofwirings 212, 321 and 322 are formed on a base plate 211. It is to beappreciated that the actual circuit board or substrate has many wiringsformed thereon but that only three wirings are shown in the drawing.Description will be made hereinafter with reference to the wiring 210 asa representative of the other wirings, for convenience unless otherwirings are required to be referred to for particular explanation.

Terminals 212 a and 212 b of the wiring 212 are formed on the circuitboard 210 or substrate to be connected with an electronic componentmounted on the circuit board 210 or external wirings. A conductiveportion 212 c is formed on the surface of or inside the circuit board210 to electrically connect the terminals 212 a and 212 b. In thisembodiment, described is a case where the circuit board 210 having theabove construction is tested as a work. It is needless to say that thework to be tested by this embodiment is not limited to theaforementioned circuit board. In this embodiment, the terminals 212 aand 212 b are provided on the respective surfaces of the circuit board210, and the conductive portion 212 c which connects the terminals 212 aand 212 b is provided inside the base plate 211. Alternatively,terminals may be formed on either one of the surfaces of the circuitboard, and a conductive portion for connecting the terminals may beformed on the same or opposite side surface of the circuit board.

The testing apparatus includes a lower fixture unit 240 which isprovided with a holding section for holding a circuit board 210 as awork thereon. The lower fixture unit 240 includes a metallic plate 241,an insulating film 242 formed on the upper surface of the metallic plate241, and a lower fixture base 245 which integrally holds the metallicplate 241 and the insulating film 242 thereon. The metallic plate 241has such a dimension as to substantially cover the lower surface of thework 210 in order to maximize a capacity provided by a wiring 212 formedon the work 210 and the metallic plate 241. The metallic plate 241 iscoated with an insulating film 242 on an upper surface thereof. Withthis arrangement, when the circuit board 210 is placed on the metallicplate 241, terminals 212 b formed on the lower surface of the circuitboard 210 are reliably kept from coming into contact with the metallicplate. The lower fixture base 245 is coupled to a lower fixture drivingmechanism 246. The lower fixture unit driving mechanism 246 drivinglyreciprocate the lower fixture unit 240 back and forth between a testposition (position shown in FIG. 8) where the work 210 is tested and aload/unload position (not shown) where the work is loaded on andunloaded from the lower fixture unit 240.

A conductive probe 281 is provided at the test position. When the lowerfixture unit 240 is moved to the test position, the metallic plate 241provided on the lower fixture unit 240 is rendered into contact with theconductive probe 281. Thus, the metallic plate 241 is electricallycommunicable with a power source 270 which is described later.

It should be noted that the insulating film 242 is not a materialelement. The metallic plate 241 is not required to be coated with theinsulating film 242 in the case of the apparatus being applied for acircuit board formed with a wiring pattern only on a top surface or acircuit board formed with an insulating layer over wiring patterns. Inthat case, the metallic plate 241 may be in direct contact with such acircuit board without the insulating film 242. Also, even if the work210 is a circuit board formed with a wiring pattern on both surfacesthereof, as will be described later, a test may be performed for such acircuit board by an apparatus which is not provided with an insulatingfilm.

An upper fixture unit 250 is arranged above the work 210. The upperfixture unit 250 is provided with a housing 251 in the form of a cap soas to cover terminals 212 a, 321 a, 321 aa and 322 a formed on the uppersurface of the work 210. The housing 251 is formed with an exhaust port254 on a side wall thereof, and is made of, e.g., a transparent silicaglass. Also, the housing 251 is provided with a seal member 252 made of,e.g., rubber on a free end of a side wall of the housing 251. Further, atransparent plate electrode 253 is attached or deposited on an innerupper surface of the housing 251.

Further, the side wall of the housing 251 may be formed by a metallicmaterial with its top wall being formed by a transparent glass. In thiscase, the metallic side wall may be used as electrode. A unit comprisedof these constituent elements 251 through 254 is operatively connectedwith an upper fixture driving mechanism 256, and is movable toward andaway from the work 210.

The upper fixture unit 250 is moved to the work 210 until the sealmember 252 on the end portion of the side wall of the housing 251 comesinto contact with the surface of the work 210. The seal member 252 isresiliently deformed against the surface of the work 210. As a result,an airtight enclosure or closed space SP is defined by the work 210, theseal member 252 and the housing 251.

The exhaust port 254 formed on the housing 251 is communicated with anexhausting device 290 via an exhaust pipe (not shown). When theexhausting device 290 is activated based on a control signal from thecontroller 201, the air inside the closed space SP is drawn out todepressurize the interior of the closed space SP to about 10⁻² atm.

It is preferable to hold the closed space SP at a vacuum degree of about10⁻² atm when a test is performed. In the case of a vacuum degree lowerthan 10⁻² atm, the electron discharge rate decreases. On the otherhands, higher vacuum degree increases the electron discharge rate.However, a longer time is required until the closed space SP reaches adesired higher vacuum degree, consequently increasing the test time.According to experiments of the inventors of the present invention, itwas confirmed that a sufficient amount of electrons are discharged underthe pressure of 10⁻² atm which can be attained in a relatively shorttime.

An electromagnetic wave irradiator 260 is provided in the apparatus toirradiate an electromagnetic wave to a terminal connected to one wiring(target wiring) alternatively selected from a plurality of wirings 212for the test. The electromagnetic wave irradiator 260 includes anelectromagnetic wave emitting section 261 which emits an electromagneticwave L in response to an operation command from the controller 201. Anelectromagnetic wave scanning section 262 directs the electromagneticwave L to a desired location on the work 210 in response to an operationcommand from the controller 201.

The electromagnetic wave emitting section 261 is constructed so as toemit ultraviolet laser light beams having a wavelength of 266 nm. Also,the electromagnetic wave emitting section 261 is provided with anoptical system to focus the laser light beams on the pad portion 212 aof a target wiring 212.

In this embodiment, the electromagnetic wave emitting section 261 emitsultraviolet laser light beams for the purpose of causing photoelectriceffect. However, this invention is not limited to the arrangement of theembodiment, and visible light beams, infrared light beams or itsequivalent may be used. The electromagnetic wave emitting section 261 isso constructed as to be driven based on a pulse signal with use of a Qswitching element and the like. The electromagnetic wave scanningsection 262 includes a galvanometer for changing the angle of a mirrorfor directing the laser light beam. The electromagnetic wave irradiator260 in accordance with this embodiment is constructed in such a mannerthat the galvanometer is driven based on an operation command from thecontroller 201 to project the electromagnetic wave L onto a desiredlocation on the surface of the work 210 accurately and speedily.

A direct current power source 270 is provided in the apparatus to applyan electric potential difference or voltage between the plate electrode253 and the metallic plate 241. The DC power source 270 outputs acertain voltage.

Further, a current detecting section 280 is provided at a position in aconductive circuit pathway through which a current runs from oneterminal of the power source 270 to the opposite terminal thereof viathe plate electrode 253, a target wiring, and the capacitive coupling ofthe metallic plate 241 and the target wiring to detect the currentrunning in the conductive pathway. Specifically, the plus terminal ofthe power source 270 is electrically connected to the plate electrode253, and the minus terminal of the power source 270 is connected to theconductive probe 281 via the current detecting section 280. Theconductive probe 281 is in contact with the metallic plate 241 when thelower fixture unit 240 and the work 210 are set at the test position.Thus, the aforementioned conductive pathway is established.

In this embodiment, an electric field of which electric potential ishigher at the plate electrode 253 than at the metallic plate 241 isgenerated when the power source 270 applies a voltage between the plateelectrode 253 and the metallic plate 241. When an electromagnetic wave Lis irradiated onto the terminal 212 a of the wiring 212 in this state,electrons are discharged from the terminal 212 a due to photoelectriceffect. The electrons discharged from the terminal 212 a areelectrically attracted by the plate electrode 253 aided by the existenceof the electric field.

Further, in this embodiment, since a certain capacity is secured by thewiring 212 and the metallic plate 241, the following effect is obtained.When electrons discharged from the wiring 212 due to photoelectriceffect are trapped by the plate electrode 253 and travel toward the plusterminal of the power source 270, the same amount of electrons as thedischarged electrons run through the metallic plate 241 from the minusterminal of the power source 270 via the current detecting section 280and the conductive probe 281. Thus, a conductive pathway along which acurrent runs from the plus terminal of the power source 270 and returnsthereto via the plate electrode 253, the wiring 212, the metallic plate241, the conductive probe 281, and the current detecting section 280 isestablished, and the current running through the conductive pathway isdetected by the current detecting section 280. The current valuedetected by the current detecting section 280 is converted into adigital signal by an A/D converter circuit 281 and sent to thecontroller 201. In this embodiment, the plate electrode 253, themetallic plate 241, and the current detecting section 280 respectivelyserve as a first electrode portion, a second electrode portion, and acurrent detector.

In this embodiment, the current detecting section 280 is providedbetween the minus terminal of the power source 270 and the conductiveprobe 281. Alternatively, as far as a current running through theaforementioned conductive pathway is detectable, the current detectingsection may be provided, for example, between the plus terminal of thepower source 270 and the plate electrode 253.

Described is a case where an electromagnetic wave L is irradiated onto aterminal 321 a of a wiring 321 as shown, e.g., in FIG. 8. In this case,the wiring 321 is a target wiring to be tested. When the target wiring321 is in a normal continuous state, the wiring 321 and the metallicplate 241 constitute a capacitor in which the terminals 321 a, 321 aa,322 b, and 321 c constitute an electrode having one polarity while themetallic plate 241 constitutes an electrode having the oppositepolarity.

When an electromagnetic wave L is irradiated onto the terminal 321 a,electrons are discharged from the terminal 321 a due to photoelectriceffect. The discharged electrons are electrically attracted and trappedby the plate electrode 253 and run to the plus terminal of the powersource 270. As a result of the electron discharge, the wiring 321 ischarged positively. On the other hand, the opposite electrode of thecapacitor, namely, the metallic plate 241 is charged negatively withelectrons being supplied from the minus terminal of the power source270. In this way, a current runs through the aforementioned conductivepathway due to irradiation of an electromagnetic wave onto the terminal321 a. Thus, the capacitor comprised of the wiring 321 and the metallicplate 241 is charged.

The waveforms a in respective graphs of FIG. 10 show changes of apotential at the wiring 321, a current running through the currentdetecting section 280 and detected thereby, and an amount of electriccharges as an integration of the currents running through the currentdetecting section 280 while the electromagnetic wave is beingirradiated. Specifically, the diagrams in FIG. 10 are graphs showingchanges of a potential at a target wiring, a current running through theaforementioned conductive pathway, and an amount of electric chargeswhich have been charged at the capacitor, before irradiation ofelectromagnetic wave and while the electromagnetic wave is beingradiated. When irradiation of an electromagnetic wave L is initiated,electrons discharged from the terminal 321 a are electrically attractedtoward the plate electrode 253 and a current runs through theaforementioned conductive pathway. As electrons are discharged from thewiring 321, the potential of the wiring 321 is raised. As a result, thecurrent running through the conductive pathway is gradually decreased.When the potential of the wiring 321 reaches the same level as the plateelectrode 253, the electrons discharged from the terminal 321 a are nolonger electrically attracted toward the plate electrode 253, andrunning of current through the conductive pathway ceases. At this time,if it is assumed that a charged amount charged at the capacitor is Q₀,the capacity of the capacitor comprised of the wiring 321 and themetallic plate 241 is C₀, and an output voltage of the power source 270is V, the following equation is established:

Q ₀ =C ₀ ·V

On the other hand, in the case where the wiring 321 is in an opencircuit state, e.g., where there is an open circuit portion at point xin FIG. 8, one electrode of the capacitor covering the areacorresponding to the terminal 321 a and a portion of the conductiveportion 321 c extending up to point x, is smaller than the electrode ofthe capacitor formed by the entire length of the wiring 321 in a normalcontinuous state. As a result, the capacity of the capacitor in the opencircuit state is smaller than the reference capacity C₀ of the capacitorin the aforementioned normal continuous state. When the terminal 321 ais irradiated with an electromagnetic wave L in the open circuit state,changes of a potential at the wiring 321, a current detected by thecurrent detecting section 280, and a charged amount charged at thecapacitor for a time upon irradiation of electromagnetic wave are, forexample, as shown by respective waveforms b in the graphs of FIG. 10.

In the case where the wiring 321 is in a short circuit state, e.g.,where there is a short-circuited portion at point y between the targetwiring 321 and the other wiring 322 in FIG. 8, the wiring 321 and theother wiring 322 constitute one electrode of the capacitor, and thecapacitance of the capacitor in the short circuit state is larger thanthe reference capacity Co of the wiring 321 in the aforementioned normalcontinuous state. When the terminal 321 a is irradiated with anelectromagnetic wave L in the short circuit state, changes of apotential at the wiring 321, a current detected by the current detectingsection 280, and an amount of electric charges that have been charged atthe capacitor for a time upon irradiation of electromagnetic wave are,for example, as shown by respective waveforms c in the graphs of FIG.10. In the case where the target wiring is in an open circuit state, theamount of electric charges corresponding to integration of the currentsthat have run through the current detecting section 280 is smaller thanthe reference charged amount Q₀, whereas in the case where the targetwiring is short-circuited with other wiring, the amount of electriccharges corresponding to integration of the currents that have runthrough the current detecting section 280 is larger than the referencecharged amount Q₀.

The controller 201 calculates the amount of the electricity Q actuallycharged at the capacitor which is calculated by integrating currentvalues measured by the current detecting section 280 whileelectromagnetic wave is being irradiated. Then, the controllerdetermines the continuity of the wiring 321 by comparing the actuallycharged amount Q with the reference charged amount Q₀ which iscalculated in advance with the wiring 321 at a normal continuous state.In this embodiment, the controller 201 has a function of determinator.

Next, an operation of the circuit board testing apparatus in accordancewith the second embodiment is described with reference to FIG. 11. FIG.11 is a flowchart showing operations of the testing apparatus shown inFIG. 8. When an untested work (circuit board) 210 is loaded on the lowerfixture unit 240 positioned at a load/unload position by a handlingdevice (not shown) incorporated in the testing apparatus or a manualoperation by an operator (in Step T1), the controller 201 start tocontrol operations of the various parts of the apparatus to execute thefollowing steps T2 to T11 so as to test shorts and open-circuits in thework 210.

When the work 210 is loaded on the lower fixture unit 240, the lowerfixture unit 240 is moved to the test position while carrying the work210 thereon (in Step T2). Thus, the work 210 is positioned at the testposition. Then, the metallic plate 241 is brought into contact with theconductive probe 281 to be connected to the current detecting section280.

Subsequently, the upper fixture unit 250 is moved to the work 210, andfixedly sandwiches the work 210 between the upper fixture unit 250 andthe lower fixture unit 240 (in Step T3). As a result, an airtight closedspace SP is defined by the housing 251, the seal member 252 and the work210. Then, the exhausting device 290 is activated to depressurize theinterior of the closed space SP to a predetermined pressure of about10⁻² atm (in Step T4). The power source 270 outputs a certain DC voltageto be applied between the plate electrode 253 and the metallic plate 241(in Step T5).

Thus, when the apparatus is set up for testing the work 210, a test asto whether a target wiring is in a normal continuous state isimplemented (in Step T6). The contents of the wiring test are describedin detail later.

Upon completion of the wiring test, the power source 270 suspends itsvoltage output (in Step T7). After suspending activation of theexhausting device 290, the air outside the apparatus is drawn into theclosed space SP (in Step T8), and the upper fixture unit 250 isretracted away from the work 210 (in Step T9), and the lower fixtureunit 240 is moved to the load/unload position (in Step T10). At a finalstage, upon verifying that the work 210 after the wiring test has beenunloaded in Step T11, the routine returns to Step T1 to execute theaforementioned series of operations.

Next, the wiring test (Step T6) is described in detail with reference toFIG. 12. FIG. 12 is a flowchart showing procedures of the wiring test tobe implemented by the apparatus.

When the routine is progressed to Step T5, the closed space SP definedby the housing 251 and the work 210 has been depressurized to apredetermined pressure of about 10⁻² atm. In this state, the controller201 controls the operative angle of the galvanometer 262 so that laserbeam is focused on the terminal 321 a of a target wiring 321 (in StepT61). The laser beam emitted from the electromagnetic wave irradiator260 is an ultraviolet laser beam having a wavelength of 266 nm.Electrons discharged from the terminal 321 a due to photoelectric effectare electrically attracted by the plate electrode 253 aided by theexistence of the electric field, and a current runs through theconductive pathway. The current is measured by the current detectingsection 280 (in Step T62). The current measurement is continued for atime (in Step T63). Next, the controller 201 calculates a charged amountof electricity based on the current values detected by the currentdetecting section 280 (in Step T64). Specifically, the charged amount Qis calculated by integrating the measured current values on time-basis.Then, the controller 201 determines whether the target wiring 321 is ina normal continuous state or other state based on the calculated chargedamount Q (in Step T65).

In other words, in the case where the charged amount Q which has beenmeasured by actual measurement falls in a predetermined allowable rangeincluding the predetermined reference charged amount Q₀ which has beencalculated in advance with respect to a wiring in a normal continuousstate as a mean value, it is judged that the target wiring 321 is in anormal continuous state. If the charged amount Q is lower than a lowerlimit of the predetermined allowable range, it is judged that the wiring321 is in an open circuit state. If the charged amount Q exceeds anupper limit of the predetermined allowable range, it is judged that thewiring 321 is in a short circuit state with respect to the other wiring.

Thus, a test with respect to a target wiring is completed. In this way,the aforementioned series of operations with respect to a wiring test isrepeated with other wirings until the test is completed with all thewirings of the work 210 (in Step T66).

As mentioned above, in the apparatus in accordance with the secondembodiment, the metallic plate 241 provides a capacitive coupling of themetallic plate 241 with the wiring or wirings to be tested. The capacityprovided by the capacitive coupling of the metallic plate 241 and thetarget wiring varies depending on whether the target wiring is incontinuity or in another state. Accordingly, the amount of electricitycharged at the capacitor comprised of the metallic plate 241 and thetarget wiring varies as the capacity varies. According to the secondembodiment, currents running through the predetermined conductivepathway via the capacitor are detected, an amount of electric chargesthat have been charged at the capacitor is calculated, and it is judgedwhether the target wiring is in a short circuit state or an open circuitstate based on the calculated charged amount. This arrangement enablesprecise and stable test of the wirings formed on a circuit board in acontactless manner.

As an alternative of the second embodiment, the testing apparatus isapplicable to testing of continuity between two terminals or two wiringsby changing a part of the aforementioned test procedures. FIG. 13 is aflowchart showing steps of the altered test executable by the testingapparatus in accordance with the second embodiment. FIGS. 14A and 14Bare sets of graphs each set showing changes of a potential at first andsecond terminals when the first and second terminals are irradiated withan electromagnetic wave, a current running through the current detectingsection 280 when the first and second terminals are irradiated, and anamount of electricity that have been charged at a capacitor for a timewhile electromagnetic wave is being irradiated and with the irradiationof electromagnetic wave being switched over from the first terminal tothe second terminal.

Since the arrangement of the testing apparatus for implementing thealtered test is identical to that of the testing apparatus in accordancewith the second embodiment, steps of the altered test are described withreference to the flowchart of FIG. 13.

In this altered test, a terminal (first terminal) 321 a, for example, isselected, and an electromagnetic wave L is irradiated onto the selectedterminal 321 a (in Step T611). Upon lapse of a time after irradiation ofthe electromagnetic wave L, for example, at a timing t1 (in Step T612),irradiation of the electromagnetic wave L is switched over to a secondterminal, for example, to a terminal 321 aa shown in FIG. 8 (in StepT613). At the same time, current values due to irradiation onto thefirst terminal 321 a and the second terminal 321 aa for respective timesare measured (in Step T614), and the measured current values areintegrated to calculate charged amounts with respect to irradiation ontothe first terminal 321 a and the second terminal 321 aa for therespective times (in Step T615). At this stage, if the first terminal321 a and the second terminal 321 aa are not in continuity, theelectrons discharged from the first terminal 321 a due to irradiation ofelectromagnetic wave onto the first terminal 321 a in Step T611 runtoward the plate electrode 253 at a high potential, whereby a currentruns through the plate electrode 253 along with potential rise of thefirst terminal 321 a. Thereafter, when irradiation of an electromagneticwave is switched over to the second terminal 321 aa in Step T613,electrons run from the second terminal 321 aa which is in a lowpotential toward the plate electrode 253 which is in a high potential.Changes of the potentials at the first terminal 321 a and the secondterminal 321 aa, the currents detected by the current detecting section280, and the charged amounts calculated by integrating the detectedcurrent values with respect to the first terminal 321 a and the secondterminal 321 aa in this state are, for example, as shown in respectivegraphs of FIG. 14A.

On the other hand, in the case where the potential of the first terminal321 a is raised by irradiation of electromagnetic wave onto the firstterminal 321 a in Step T611 when the first terminal 321 a and the secondterminal 321 aa are in continuity, the potential of the second terminal321 aa which is in continuity with respect to the first terminal 321 ais also raised. In this state, even if the second terminal 321 aa isirradiated with an electromagnetic wave in Step T613, electronsdischarged from the second terminal 321 aa are not electricallyattracted toward the plate electrode 253, and an electric fieldresulting from attraction of electrons is not generated. As a result,the electrons do not travel toward the plate electrode 253, and thecurrent value detected by the current detecting section 280 is zero orexceedingly lower than the current value detected in the case where thefirst terminal 321 a and the second terminal 321 aa are in continuity.The potentials at the first terminal 321 a and the second terminal 321aa, the currents detected by the current detecting section 280 withrespect to the first terminal 321 a and the second terminal 321 aa, andthe charged amounts obtained by integrating the detected currents whenirradiation is switched over from the first terminal 321 a to the secondterminal 321 aa in this state are, for example, as shown in respectivegraphs of FIG. 14B.

Upon completion of current measurements, the controller 201 calculates achange of the charged amount Q on a time-basis by integrating thecurrent values detected by the current detecting section 280 (in StepT616), and determines whether the first terminal 321 a and the secondterminal 321 aa are in continuity based on the result of calculation (inStep T617). Specifically, in the case where the actually measuredcharged amount Q varies before and after the timing t1, as shown in FIG.14A, it is judged that the first terminal 321 a and the second terminal321 aa are not connected with each other. On the other hand, in the casewhere the changed amount Q does not vary before and after the timing t1,as shown in FIG. 14B, it is judged that the first terminal 321 a and thesecond terminal 321 aa are connected with each other. Thus, a test withrespect to one target wiring is completed. The aforementioned series ofoperations with respect to the wiring test are repeated until the testis completed with respect to all the wirings of the work 210 (in StepT618).

In the above embodiment, described is the case where the test isperformed between the first terminal 321 a and the second terminal 321aa which are designed to be continuous with each other as shown in FIG.8. In this case, if the terminals 321 a and 321 aa are in continuity, itis judged that the wiring test between the terminals 321 a and 321 aahas “PASSED”, whereas if the terminals 321 a and 321 aa arediscontinuous, it is judged that the terminals 321 a and 321 aa are inan open circuit state.

On the other hand, in the case where the test is performed by selectingterminals which are not designed to be continuous, e.g., in the case ofthe terminals 321 a and 322 a, if the terminals 321 a and 322 a are indiscontinuity, it is judged that the wiring test between the terminals321 a and 322 a has “PASSED”, whereas if the terminals 321 a and 322 aare in continuity, it is judged that the terminals 321 a and 322 a arein a short circuit state. Thus, in the testing apparatus in accordancewith the second embodiment, a judgment as to whether an arbitrarycombination of terminals of wirings formed on a circuit board is incontinuity or discontinuity enables one to test open-circuits and shortsin the wirings.

As mentioned above, in the second embodiment, an electromagnetic wave isselectively irradiated on a plurality of terminals one after another,and it is judged whether the selected pair of terminals is in continuityor not based on a change of an amount of electric charges that have runthrough and detected by the current detecting section 280 before andafter the irradiation is switched over between the pairs of terminals.In this embodiment, a high potential is applied to the plate electrode253 which is provided in the vicinity of the terminals to securely allowthe plate electrode 253 to trap electrons discharged from the terminals.This arrangement enables to precisely and stably test opens andshorts-circuit of the selected pairs of terminals.

In this embodiment, measured is a current that has run through thecurrent detecting section 280 with the irradiation being switched overfrom the first terminal to the second terminal. Alternatively, it may bepossible to allow the current detecting section 280 to keep on measuringa current for some time before the selected first terminal is irradiatedso as to integrate the charged amount.

In this embodiment, it is required to monitor the current for a timeperiod from the start of current flow until the current flow issuspended so as to calculate a charged amount Q for the monitored timeby integrating the monitored current values. In view of this, thisembodiment adopts a technique of securely detecting travel of electriccharges by continuously measuring currents for a time being while theelectromagnetic wave is being irradiated. Alternatively, change ofcurrents may be monitored until the current falls down to apredetermined level, current may be measured continuously until thecurrent or its integration becomes lowered than a predetermined value.

In the second embodiment, the amount of charge Q is calculated byintegrating current values on time-basis to judge whether the targetwiring is in continuity based on the calculated charged amount Q.Alternatively, a peak value of current may be detected to judge whetherthe detected peak value is lower than a reference value or to count atime until the detected current falls to a predetermined level so as todetermine whether the target wiring is in continuity.

Alternatively, a test may be performed by combining the test made in thesecond embodiment and any of the above mentioned alternative tests. Asan example, the following arrangement is appreciated. An electromagneticwave is irradiated onto the first terminal to perform a test withrespect to a wiring (target wiring) connected to the first terminal.When the target wiring is judged to be in an open or short circuitstate, it is subsequently tested whether the target wiring relative tothe other wirings are in continuity. This arrangement enables detectionof the portion and the nature of the defect of the tested circuit board.

As mentioned above, there is a case that a test by a testing apparatuswhich is not provided with an insulating film 242 is advantageous evenif a work 210 is a circuit board having wirings on the opposite sidesthereof. This is because a wiring 212 connected to a terminal 212 bfunctions as part of the second electrode portion by allowing theterminal 212 b which is formed on the lower surface of the circuitboard, to be electrically connected to a metallic plate 241 in the casewhere such a circuit board is rendered into direct contact with themetallic plate 241. In view of this, in the case where the work 210 is,for example, a circuit board having a lower surface formed with a groundlayer, or a circuit board in which a terminal to be connected to aground layer formed inside the circuit board is provided on the lowersurface of the circuit board, it is possible to function the groundlayer as part of the second electrode portion by rendering the work 210into direct contact with the metallic plate 241. At this time, thecapacity of the capacitor comprised of the target wiring and the secondelectrode portion can be raised, and the current running through thecapacitor can be increased with the result that detection of the currentby the current detecting section 280 is facilitated.

Further, since the position of the target wiring relative to the secondelectrode portion is clearly determined, a variation of capacity of thecapacitor comprised of the target wiring and the second electrodeportion is lessened. As a result, a precise and stable test can beperformed.

In the second embodiment, providing the metallic plate 241 on the lowerfixture unit 240 to oppose the metallic plate 241 to the work 210 andconnecting the metallic plate 241 to the power source 270 enables themetallic plate 241 to function as the second electrode portion. Forexample, in the case where the work 210 is a multi-layered substrate inwhich each of a plurality of layers formed with a wiring pattern areplaced one over another, it is impossible to secure a sufficientcapacity between a target wiring and the metallic plate 241 because theother wirings, a power source, or a ground layer may intervene betweenthe target wiring and the metallic plate 241. As a result, it is highlylikely that a precise and stable test cannot be performed. In such acase, functioning the wiring formed in the circuit board, e.g., theground layer as the second electrode portion enables one to perform awiring test precisely and stably.

FIG. 15 is a diagram showing a testing apparatus as a first modificationof the second embodiment in which a ground layer formed in a circuitboard functions as the second electrode portion.

The testing apparatus as the first modification is adapted to test theelectric state of a circuit board 220. As shown in FIG. 15, the circuitboard 220 is formed with a plurality of wirings 222 on a base plate 221.Each wiring 222 includes terminals 222 a and 222 b which are formed onthe respective opposite surfaces of the circuit board 220, and aconductive portion 222 c which is formed on the surface or inside thecircuit board 220 and is electrically connected to the terminals 222 aand 222 b. A ground layer 223 is provided inside the base plate 221 toapply a reference potential to an electronic circuit established on thecircuit board 220 to implement predetermined operations of theapparatus. The ground layer 223 extends substantially over the entiresurface of the circuit board 220 except portions allowing passage of theconductive portions such as 222 c, and is connected to a terminal 223 awhich is formed on the upper surface of the circuit board 220 so as tobe electrically connected to an external ground. In this modification,described is a case where the circuit board 220 having the aboveconstruction is used as a work to be tested by the testing apparatus ofthe first modification. It is needless to say that the work to be testedby the apparatus is not limited to the aforementioned circuit board. Theinventive apparatus may test a circuit board, for example, in which aground layer 223 is a conductive member in the form of a mesh.

In this modification, a lower fixture unit 240 includes a non-conductivesupport block 243, whereas in the arrangement of the second embodiment,the lower fixture unit 240 includes the metallic plate 241 and theinsulating film 242 as shown in FIG. 8. The arrangement of themodification is advantageous in that the modification does not requirean electrode having a large surface area in the lower fixture unit 240since the ground layer 223 formed inside the circuit board 220 serves asthe second electrode portion. It should be appreciated that thearrangement of the second embodiment shown in FIG. 8 also enables one toperform the same test as in this modification.

Similar to the testing apparatus in accordance with the secondembodiment, the modified apparatus is constructed in such a manner thatan upper fixture unit 250 is moved toward the work 220 to securely holdthe work 220 between the upper fixture unit 250 and the lower fixtureunit 240, whereby an airtight closed space SP is defined by a housing251, seal member 252 and the work 220. The housing 251 is so constructedas to expose the terminal 223 a connected to the ground layer 223,outside the closed space SP. A conductive probe 257 is provided on theupper fixture unit 250 to be connected to a current detecting section280. The conductive probe 257 is rendered into contact with the terminal223 a connected to the ground layer 223 of the work 220 as the upperfixture unit 250 is moved to the work 220 positioned at a test position,thereby securing electric connection between the ground layer 223 andthe current detecting section 280. In this modification, since it is notrequired to provide electric connection between the lower fixture unit240 and the current detecting section 280, a conductive probe 281 whichis provided in the apparatus of the second embodiment as shown in FIG. 8is omitted. Since the arrangement of the first modification of thesecond embodiment is substantially identical to the arrangement of thesecond embodiment shown in FIG. 8 except the above mentionedconfiguration, the elements of the first modification which areidentical to those of the second embodiment are denoted with the samereference numerals, and a description thereof is omitted herein.

In this modification, the ground layer 223 is electrically connected tothe current detecting section 280 via the conductive probe 257. Each ofthe wirings 222 formed on the circuit board is capacitively coupled tothe ground layer 223. In this way, the ground layer 223 satisfies arequirement as the second electrode portion, namely, the requirementthat the second electrode should be connected to an external powersource and capacitively coupled to a target wiring inside the circuitboard. Thus, the ground layer 223 can function as the second electrodeportion in the first modification.

Operations of the testing apparatus as the first modification are thesame as those of the testing apparatus in accordance with the secondembodiment as shown in FIG. 8 except the following.

Specifically, in the first modification, a current due to photoelectriceffect runs through the current detecting section 280 from the groundlayer 223 via the conductive probe 257, whereas in the secondembodiment, a current runs through the current detecting section 280from the metallic plate 241 via the conductive probe 281. The otheroperations of the testing apparatus in the first modification are thesame as the testing apparatus in accordance with the second embodimentshown in FIG. 8. The first modified testing apparatus enables one toprecisely and stably test whether a target wiring is in a short circuitstate or an open circuit state, and test as to whether there iscontinuity between a selected pair of terminals.

In the first modification, it is judged whether each wiring is in ashort circuit state or an open circuit state based on an amount ofelectric charges that have been charged in a capacitor comprised of theground layer 223 and each wiring. Thus, since the target wiring and thesecond electrode portion are provided on the same circuit board, thereis no likelihood that the capacity may vary due to a positionaldisplacement of the circuit board relative to the lower fixture unitwhen placing the circuit board to a test position, a warp or a variationof thickness over the entirety of the circuit board. As a result, thisarrangement enables to perform a wiring test precisely and stably.

In this modification, described is the case where the terminal 223 aconnected to the ground layer 223 is formed on the upper surface of thecircuit board 220. This invention is applicable to a modification otherthan the aforementioned modification. For instance, as far as thecircuit board 220 has a ground terminal on the lower surface thereof, itmay be possible to electrically connect a ground layer 223 to a powersource 270 or allow a conductive probe 257 to come into contact with theground terminal through the lower surface of the work 220 byconstructing a lower fixture unit with a metallic plate 241 which is notformed with an insulating film and rendering the ground terminal intocontact with the metallic plate 241.

In this modification, the ground layer formed inside the circuit board220 serves as the second electrode portion. Alternatively, a groundplane which is so formed as to cover generally an entirety of onesurface of a circuit board, or a wiring other than the ground layerformed in the circuit board, e.g., a wiring serving as a power line maybe used as the second electrode portion.

FIG. 16 is a diagram showing a testing apparatus as a secondmodification of the second embodiment of the invention. The arrangementand operations of the testing apparatus in the second modification arebasically the same as those of the testing apparatus in accordance withthe second embodiment shown in FIG. 8. However, the manner of capturingthe photoelectron is different between the second modification and thesecond embodiment, and part of the arrangement of the secondmodification differs from the second embodiment in association with thedifference in the manner of photoelectron capturing. Accordingly, onlythe differences between the second modification and the secondembodiment are described herein. Elements of the second modificationwhich are identical to those of the second embodiment are denoted withthe same reference numerals, and a description thereof is omittedherein.

The testing apparatus as the second modification of the secondembodiment is adapted for testing an electric state of a circuit board230. As shown in FIG. 16, the circuit board 230 is constructed in such amanner that a plurality of wirings 232 are formed on a base plate 231.Each wiring 232 includes terminals 232 a and 232 b which are formed onthe respective opposite surfaces of the circuit board 230 to beconnected to an electronic component mounted on the circuit board or anexternal wiring, and a conductive portion 232 c which is formed on thesurface or inside the circuit board 230 to be connected to the terminals232 a, 232 b. In this modification, described is a case where thecircuit board 230 having the above construction is used as a work to betested by the testing apparatus. It is needless to say that the work isnot limited to the above circuit board.

In this modification, similar to the testing apparatus in accordancewith the second embodiment shown in FIG. 8, an upper fixture unit 250 ismoved toward the work 230 to securely hold the work 230 between theupper fixture unit 250 and the lower fixture unit 240, whereby anairtight closed space SP is defined by a housing 251, a seal member 252and the work 230. The housing 251 is so constructed as to expose aterminal 233 b-1 of a wiring 233 b including the terminal 233 b-1 and aterminal 233 b-2, outside the closed space SP and accommodate theterminal 233 b-2 inside the closed space SP. The upper fixture unit 250is provided with a conductive probe 258, and is connected to the plusterminal of a power source 270. The conductive probe 258 is adapted toelectrically connect the terminal 233 b-1 and the plus terminal of thepower source 270 as the upper fixture unit 250 is moved to the work 230positioned at the test position. Thereby, a voltage of the power source270 is applied between the wiring 233 b connected to the terminal 233b-1 and a metallic plate 241 serving as the second electrode portion ofthis invention. When the voltage is applied, an electric field isgenerated in the vicinity of the terminal 233 b-2 which is connected tothe wiring 233 b and is accommodated in the closed space SP. Then, whena controller 201 selects a wiring 233 a as a target wiring, and anelectromagnetic wave irradiator 260 irradiates an electromagnetic wave Lonto a terminal potion 233 a-1 of the target wiring 233 a, electrons aredischarged from the terminal 233 a-1 and electrically attracted andcaptured on the terminal 233 b-2 aided by the existence of the electricfield. As a result, a current runs through the power source 270 via theconductive probe 258. At this time, electrons run through the metallicplate 241 which is capacitively coupled to the target wiring 233 a, fromthe power source 270 via the current detecting section 280 and theconductive probe 281. As a result, a current is detected by the currentdetecting section 280. Thus, a wiring test can be performed by thetesting apparatus of the second modification in the similar manner asthe testing apparatus in accordance with the second embodiment of theinvention.

As mentioned above, in the second modification of the second embodiment,the upper fixture unit 250 is constructed in such a manner that theterminal 233 b-1 of the wiring 233 b formed on the circuit board 230 isexposed outside the closed space SP, and the opposite terminal 233 b-2of the wiring 233 b is housed inside the closed space SP. Electricallyconnecting the terminal 233 b-1 to the power source 270 via theconductive probe 258 in the above arrangement enables the wiring 233 bto function as the first electrode portion to capture the photoelectrondischarged from the terminal irradiated by electromagnetic wave. As aresult, this modification does not require a plate electrode 253 whichis provided in the testing apparatus in accordance with the secondembodiment shown in FIG. 8, and the housing 251 is so configured as tosecure a minimal surface area for covering the terminal of a wiring tobe tested with respect to the work 230. Accordingly, this arrangementenables a smaller testing apparatus while reducing a volume of theclosed space SP which is subjected to depressurization. Thus, a wiringtest can be performed in a shorter time because a time required fordepressurization is shortened due to the reduced volume of the closedspace SP.

This invention is not limited to the aforementioned embodiments andmodifications. Various modifications and alterations can be provided.For instance, in the second embodiment and its modifications, describedis the case where the interior of the housing is depressurized.Alternatively, a depressurization may not be required or the vacuumdegree may be varied as the case may be. Further, in the secondembodiment and its modifications, the housing is so configured as tocover the terminal of the target wiring formed on the surface of thecircuit board so as to irradiate an electromagnetic wave onto theterminal. Alternatively, there may be provided an arrangement in which aclosed space is defined by fitting contact of an outer circumferentialportion of a housing with an outer circumferential portion of a lowerfixture unit and the entirety of a circuit board is housed in the closedspace for depressurization. As a further altered form, a housing may beso configured as to house a circuit board and a lower fixture unit as awhole so as to depressurize the entire interior of the housing.

Further, combination of the modifications of the second embodiment maybe applicable. For instance, combining the first modification and thesecond modification enables a wiring formed on a circuit board (i.e.,work) which is connected to a power source to function as the firstelectrode portion and a ground layer formed on the circuit board tofunction as the second electrode portion so as to perform a wiring test.

As mentioned above, in the second embodiment and its modifications,since a high potential is applied to the first electrode portion whichis disposed in the vicinity of the terminal to be connected to thetarget wiring, electrons discharged from the terminal due tophotoelectric effect upon irradiation of an electromagnetic wave aresecurely attracted and trapped on the first electrode portion.Furthermore, since the second electrode portion is so arranged as to becapacitively coupled to the target wiring, the electrons that have runthrough the first electrode portion are securely detected as a currentrunning through a closed circuit via the capacitor comprises of thetarget wiring and the second electrode portion. Thus, a wiring test isperformed based on the detected current. This arrangement enablestesting of open circuits and short circuits in the target wiring withoutelectric contact of both surfaces of the circuit board with the upperand lower fixtures.

FIG. 17 is a diagram showing a circuit board testing apparatus inaccordance with a third embodiment of the invention. FIG. 18 is a blockdiagram showing an electric configuration of the testing apparatus inFIG. 17. A circuit board testing apparatus is adapted to test a circuitboard 410 which is capable of mounting thereon a semiconductor chipaccording to C4 (Controlled Collapse Chip Connection) package method.

As shown in FIG. 17, the circuit board 410 is constructed in such amanner that a plurality of wirings as represented by the wiring 412 areformed on a base plate 411. Each wiring 412 includes a pad portion 412 aformed on one surface of the base plate 411 to be connected with a padon a semiconductor chip, a ball grid portion 412 b formed on theopposite surface of the base plate 411, and a conductive portion 412 carranged on or in the base plate 411 to electrically connect the padportion 412 a and the ball grid portion 412 b. The pad portions 412 aare arranged at small pitches to correspond to the pitches of the padsof semiconductor chips, whereas the ball grid portions 412 b arearranged at larger pitches as compared to the pitches of the padportions 412 a. The pad portions 412 a are gathered in a region ER onone surface of the circuit board 410. The region ER is a wiring endexposure area. In this embodiment, the circuit board 410 having theabove construction is referred to as a work to be tested by theapparatus. However, it is needless to say that a circuit board to betested by the present embodiment is not limited to the above.

The apparatus includes a work holder 421 to carry a piece of circuitboard as a work 410. The work holder 421 is movable between a testposition (position shown in FIG. 17) where the work 410 is tested and aload/unload position (not shown) where the work 410 is loadable to thework holder 421 or unloadable from the work holder 421. A work drivingmechanism 422 drivingly reciprocate the work holder 421 back and forthbetween the test position and the load/unload position in response to acontrol signal from a controller 430 which controls an overall operationof the apparatus.

A lower fixture unit 440 is provided below the work 410 at the testposition. The lower fixture unit 440 includes a plurality of conductivespring probes 441 which are arranged to respectively connected with thecorresponding ball grid portions 412 b of the respective wirings 412.The lower fixture is further provided with a multiplexer 442, and alower fixture base (not shown) which is movable toward and away from thework 410 while holding the probes 441 and the multiplexer 442 thereon.The lower fixture base is coupled to a lower fixture unit drivingmechanism 445. The lower fixture unit driving mechanism 445 drivinglymoves the lower fixture base toward and away from the work 410 inaccordance with a control signal from the controller 430.

An upper fixture unit 450 is arranged above the work 410 at the testposition. The upper fixture unit 450 includes a cap-like housing of atransparent glass which is formed with an exhaust port 454, and is soconfigured as to cover the wiring exposure area ER on the work 410. Theupper fixture 450 further includes a seal member 452 mounted on an endportion of a side wall of the housing 451, and a transparent electrode453 mounted on an inner upper surface of the housing 451. Thetransparent electrode 453 extends in two dimensions to substantiallycover the wiring exposure area ER. These elements 451 through 454 areintegrally movable toward and away from the work 410. An upper fixtureunit driving mechanism 456 is coupled to the upper fixture unit 450. Theupper fixture unit 450 is moved toward and away from the work 410 inresponse to a control signal from the controller 430.

The upper fixture unit 450 is moved to the work 410 until the sealmember 452 of the housing 451 comes into contact with the surface of thework 410. As a result, the seal member 452 is resiliently deformed whilebeing pressingly sandwiched between the bottom edge of the side wall ofthe housing 451 and the surface of the work 410. Consequently, anairtight closed space SP is defined by the work 410, the seal member452, and the housing 451.

The exhaust port 454 formed in the housing 451 is communicated with anexhausting device 490 via an exhaust pipe (not shown). When theexhausting device 490 is activated based on a control signal from thecontroller 430, the air inside the closed space SP is exhausted tothereby render the interior of the closed space SP to a depressurizedstate. When a test is performed, the closed space SP is preferably heldat a vacuum degree of about 10⁻² atm as is the same as in the abovedescribed embodiments.

A power source 460 is provided in the apparatus to apply a certain DCvoltage to a target wiring. The plus terminal of the power source 460 iselectrically connected to the transparent electrode 453, and the minusterminal thereof is connected to the multiplexer 442 via a currentdetecting section 480. The multiplexer 442 is operated to select a ballgrid portion of a wiring in response to a selection command from thecontroller 430. In this configuration, when, for example, as shown inFIG. 17, a ball grid portion 521 b of a wiring 521 is selected based ona selection command from the controller 430, a DC voltage of the powersource 460 is applied between the ball grid portion 521 b and thetransparent electrode 453. In this case, the wiring 521 is a targetwiring to be tested. A current value measured by the current detectingsection 480 is converted into a digital signal by an A/D convertercircuit 481, and sent to the controller 430. Thereupon, the controller430 determines whether the target wiring is in continuity or not basedon the measured current value while controlling an overall operation ofthe apparatus.

A UV lamp 470 is provided above the upper fixture unit 450. A lampcontrol circuit 471 controls the UV lamp 470 to turn on and off based ona control signal from the controller 430. The UV lamp 470 emits anultraviolet laser light beam L toward the upper surface of the housing451. An ultraviolet laser light beam L emitted from the UV lamp 470passes through the upper surface of the housing 451 and the transparentelectrode 453, and is incident upon the wiring exposure area ER on thework 410.

In this embodiment, the UV lamp 470 is used as an electromagnetic waveirradiator. Alternatively, as far as an element is capable of causing aconductive member of a wiring on a circuit board to exhibit aphotoelectric effect, such an element is usable as an electromagneticwave irradiator. The UV lamp 470 is operable to emit ultraviolet laserlight beams having a wavelength of 266 nm.

In this embodiment, ultraviolet laser light beams are emitted using theUV lamp 470 for the purpose of raising the photoelectric effect.However, this invention is not limited to a UV lamp, and visible lightbeams, infrared light beams or its equivalent may be used.

Next, an open circuit test with respect to a wiring by the testingapparatus in accordance with the third embodiment is described withreference to FIGS. 20 and 21. FIG. 20 is a flowchart showing operationsof the circuit board testing apparatus shown in FIG. 17. When anuntested work (circuit board) 410 is loaded on the work holder 421 atthe load/unload position by a handling device (not shown) incorporatedin the testing apparatus or a manual operation by an operator (in StepU1), the controller 430 starts to control operations of the variousparts of the apparatus to execute the following steps U2 to U12 so as totest open-circuit of the wirings on the work 410.

First, the work holder 421 clamps the work 410 thereon in Step U2. Then,while holding the work 410 thereon, the work holder 421 is moved to thetest position (position shown in FIG. 17) where the work 410 is tested(in Step U3). Thus, the work 410 is positioned at the test position.

Subsequently, the upper fixture unit 450 and the lower fixture unit 440are moved to the work 410 (in Step U4). As the lower fixture unit 440 ismoved to the work 410, as shown in FIG. 17, lead ends of conductivespring probes 441 are pressed against respective corresponding ones ofthe ball grid portions 412 b of the wirings 412 to be electricallyconnected thereto. Simultaneously, the upper fixture unit 450 is movedto the test position, as shown in FIG. 17 to securely holds the work 410between the upper fixture unit 450 and the lower fixture unit 440. Next,an exhausting device 490 is activated to depressurize the interior ofthe closed space SP defined by the housing 451, the seal member 452 andthe work 410 (in Step U5).

Thus, when the apparatus is set up for testing the work 410, the UV lamp470 is turned on to irradiate an ultraviolet laser light beam L onto thewiring exposure area ER (in Step U6). Then, the apparatus implements anopen circuit test with respect to the target wiring (in Step U7) to testthe work 410. The open circuit test are described later in detail.

Upon completion of the open circuit test, the UV lamp 470 is turned off(in Step U8). Then, the activation of the exhausting device 490 issuspended, and the air outside the apparatus is drawn into the closedspace SP (in Step U9). Subsequently, the lower fixture unit 440 and theupper fixture unit 450 are moved away from the work 410 (in Step U10),and the work holder 421 releases clamping the work 410 and is retractedto the load/unload position (in Step U11). Lastly, when it is verifiedthat the work 410 after the open circuit test is unloaded from the workholder 421 (in Step U12), the routine returns to Step U1 to implementthe aforementioned series of operations.

Next, the open circuit test with respect to a wiring to be implementedby the apparatus in accordance with the third embodiment (Step U7) isdescribed in detail with reference to FIG. 20. FIG. 20 is a flowchartshowing an open circuit test with respect to a wiring to be implementedby the circuit board testing apparatus in accordance with the thirdembodiment. After the UV lamp 470 is turned on in Step U6, themultiplexer 442 selects an arbitrary wiring 521 as a target wiring inaccordance with a selection command from the controller 430 toelectrically connect the target wiring 521 to the power source 460, anda voltage is applied between the ball grid portion 521 b of the targetwiring 521 and the transparent electrode 453 (in Step U71). Upon lapseof a time until the power supply is stabilized (in Step U72), thecurrent detecting section 480 measures a current running therethrough(in Step U73). When a voltage is applied between the ball grid portion521 b and the transparent electrode 453 in a state that the targetwiring 521 is in continuity, an electric field is generated between thetransparent electrode 453 and the pad portion 521 a. At this time,electrons discharged from the pad portion 521 a due to photoelectriceffect are electrically attracted and captured by the transparentelectrode 453 aided by the existence of the electric field. As a result,a photocurrent I_(O) runs through a conductive pathway which isestablished from the plus terminal of the power source 460 to the minusterminal thereof via the transparent electrode 453, the target wiring521, the multiplexer 442, and the current detecting section 480, and isdetected by the current detecting section 480. On the other hand, in thecase where the target wiring 521 is in an open circuit state, theaforementioned conductive pathway is not established, and the currentvalue detected by the current detecting section 480 is zero orexceedingly lower than a current detected in the case where the targetwiring 521 is in continuity.

In this way, the controller 430 determines, as mentioned below, whetherthe target wiring is in an open circuit state or not based on thecurrent value detected by the current detecting section 480 (in StepU74). Specifically, in the case where the photoelectric current I_(O)detected by the current detecting section 480 is equal to or greaterthan a predetermined threshold value I1, it is judged that the targetwiring is continuous. On the other hand, if the photocurrent I_(O) islower than the threshold value I1, it is judged that the target wiringis discontinuous. In this way, in the third embodiment, the controller430 has a function of a determinator as well as other function ofcontrolling the operation of the apparatus. The threshold value I1 isdetermined as follows. Since the magnitude of photoelectric current isdetermined by multiplying intensity of irradiated electromagnetic wavei.e. light by the surface area of a conductive member irradiated withthe light, the threshold value I1 is selected from a range smaller thana minimal current value which is theoretically calculated based onintensity of an ultraviolet laser light beam L and the surface area ofthe pad portion 412 a and larger than a noise current value in order tosecurely distinguish the photoelectric current from the other noisecurrents.

In this way, when an open circuit test with respect to one wiring iscompleted, the routine returns to Step U71 to implement the open circuittest of another wiring. Thus, the aforementioned series of operationsare repeated until the test is completed with respect to all the wiringsof the circuit board.

As mentioned above, the apparatus shown in FIG. 17 is similar to theprior art arrangement in the aspect of testing whether a wiring is in anopen circuit state by utilizing photoelectric effect. However, theapparatus of the third embodiment has the feature that a plurality ofpad portions 412 a formed on the upper plane of the work 410 areirradiated with ultraviolet laser light beams. The apparatus isadvantageous in that an open circuit test can be performed with asimplified apparatus and within a short time without requiring anarrangement of focusing or scanning ultraviolet laser light beams.

Generally, a wiring formed on a circuit board defines a capacitor havinga floating capacity between the wiring and a GND pad or between thewiring and the other wiring. Consequently, when a voltage is applied, atransient current runs through the wirings in an attempt to charge thecapacitor. As a result, it is highly likely that an erroneous judgmentis made resulting from erroneous detection of a transient current by thecurrent detecting section 480. In view of this, this embodiment employsan arrangement in which a current is measured after implementing StepU72, namely, upon lapse of a certain stand-by time from application of avoltage until a current is stabilized. The additionally providedstand-by time, however, may extend a time required for a test. In viewof this, the following first modification of the third embodiment isdevised in order to shorten the test time.

FIG. 21 is a diagram showing a testing apparatus as the firstmodification of the third embodiment to suppress a transient current soas to shorten the stand-by time. The first modification is differentfrom the third embodiment in that in the first modification, respectiveswitch portions of a multiplexer 442 include normal close (NC) contactsand that the wirings other than a target wiring are connected to theminus terminal of a power source 460 bypassing a current detectingsection 480 through the NC contacts. The first modification is similarto the third embodiment in that a wiring 521 selected as a target wiringis connected to the current detecting section 480 through a normal open(NO) contact. Since an arrangement of the first modification isidentical to that of the third embodiment except the above points,elements of the first modification which are identical to those of thethird embodiment are denoted at the same reference numerals, and adescription thereof is omitted herein.

Operations of the first modification are substantially the same as thoseof the testing apparatus shown in FIG. 17 (as shown in the flowcharts ofFIGS. 19 and 20) except the following points. Specifically, in the firstmodification, when a voltage is applied between a ball grid portion 521b of a target wiring 521 and a transparent electrode 453, an electricfield is generated between pad portions 522 a, 523 a of the otherwirings to which a GND potential or ground potential is applied, and thetransparent electrode 453. As a result, electrons discharged from thepad portions 521 a, 522 a and 523 a due to photoelectric effect areelectrically attracted and captured by the transparent electrode 453,whereby a current runs through the wirings. The current running throughthe target wiring 521 is guided to the current detecting section 480 viathe NO contact of the switch portion 443 a of the multiplexer 442. Onthe other hand, the currents running through the other wirings 522, 523are guided to the minus terminal of the power source 460 via therespective NC contacts of the switch portions 443 b and 443 c of themultiplexer 442. This arrangement enables to eliminate a drawback that atransient current which has undesirably run through the other wirings522 and 523 may run through the current detecting section 480, andeliminates a likelihood that the transient current may adversely affectcurrent detection by the current detecting section 480.

As mentioned above, the testing apparatus shown in FIG. 21 is soconstructed as to keep a current running through the wirings other thanthe target wiring from running through the current detecting section480. This arrangement eliminates an erroneous judgment resulting fromrunning of a transient current through the current detecting section 480even if the stand-by time is shortened, and consequently shortens a timerequired for a test as a whole.

The manner of suppressing running of a transient current described inthe above first modification can be modified as shown in the followingsecond and third modifications.

In the above, description is made about the open circuit test of awiring, implemented by the circuit board testing apparatus according tothe third embodiment. The apparatus according to the third embodimentcan perform a short circuit test of the wirings by supplying testsignals through the ball grid portions. For example, if the plusterminal of the power source 460 is connected to the ball grid connectedto the wiring 523 and the minus terminal of the power source isconnected to the ball grid connected to the wiring 522, then, the shortcircuit between the wirings 523 and 522 is detected. According to thesecond and third modifications of the third embodiment, an open circuittest with respect to a target wiring, and a short circuit test withrespect to the target wiring relative to the other wiring can beperformed simultaneously.

FIG. 22 is a diagram showing a circuit board testing apparatus as asecond modification of the third embodiment, and FIG. 23 is a flowchartshowing operations of an open/short circuit test by the apparatus shownin FIG. 22. The second modification is different from the thirdembodiment in that in the second modification, respective switchportions 443 of a multiplexer 442 have normal close (NC) contacts, andthat wirings other than a target wiring are connected to the plusterminal of a power source 460 via the NC contacts. The secondmodification is similar to the third embodiment in that the wiringselected as the target wiring is connected to a current detectingsection 480 via a normal open (NO) contact. Since the arrangement of thesecond modification is identical to that of the third embodiment exceptthe above points, elements of the second modification which areidentical to those of the third embodiment are denoted with the samereference numerals, and a description thereof is omitted herein.

Operations of the second modification are substantially the same asthose of the testing apparatus shown in FIG. 17 (as shown in theflowchart of FIG. 19) except that the open/short circuit test operationshown in FIG. 23 is executed in the second modification in place of theopen circuit test implemented in Step U7 of FIG. 19. The operations ofthe second modification are described with reference to FIGS. 19, 22,and 23.

When a UV lamp 470 is turned on in Step U6 of FIG. 19, each wiring isconnected to the plus terminal of the power source 460 via each NCcontact of each switch portion 443 of the multiplexer 442 to apply thesame potential thereto as the transparent electrode 453. Next, themultiplexer 442 selects one wiring 521 in response to a selectioncommand from a controller 430 in Step U711 (namely, the switch portion443 a is switched over to the NO contact) to connect the wiring 521 tothe current detecting section 480. As a result, merely the wiring 521 isset to a low potential. Upon lapse of a time until a fluctuation ofcurrent detection due to a transient current becomes negligible (in StepU712), the current detecting section 480 measures a current runningtherethrough (in Step U713).

Here, described is a case where the wiring 521 is short-circuited withone of the other wirings 521 and 523. For instance, in the case wherethe wiring 521 is short-circuited with the wiring 522 at a portion yshown by the dotted line in FIG. 22, a conductive pathway is establishedthrough which a current runs from the power source 460 and is returnedthereto via the wiring 522, the short-circuited portion y, the targetwiring 521 and the current detecting section 480. As a result, ashort-circuit current I_(S) runs through the conductive pathway, and thecurrent value is measured by the current detecting section 480.

On the other hand, in the case where the wiring 521 is notshort-circuited with the other wiring, a current value measured by thecurrent detecting section 480 is determined based on presence or absenceof an open circuit portion in the wiring 521 as in the case of theapparatus shown in FIG. 17. If the wiring 521 is in a normal continuousstate (namely, there is no open circuit portion in the wiring 521 and noshort circuit portion in the wiring 521 relative to the other wiring), aphotoelectric current I_(O) runs through the current detecting section480. On the other hand, if there is a short-circuited portion betweenthe wiring 521 and at least one of the other wirings, a short circuitcurrent I_(S) runs through the current detecting section 480. Further,if there is an open circuit portion in the wiring 521, the currentmeasured by the current detecting section 480 is zero or exceedinglylower than the current due to the photoelectric current I_(O).

As mentioned above, generally, a short circuit current I_(S) isdistinguishably larger than the photoelectric current I_(O).Accordingly, the controller 430 determines whether the target wiring isin an open circuit state or a short circuit state based on the currentin Step U714. Specifically, if the current value detected by the currentdetecting section 480 is lower than a threshold value I1, it is judgedthat the wiring 521 is in an open circuit state. If the current valuedetected by the current detecting section 480 is not smaller than thethreshold value I1 and smaller than a threshold value I2, it is judgedthat the wiring 521 is in a normal continuous state. On the other hand,if the current value detected by the current detecting section 480 isnot smaller than the threshold value I2, it is judged that the wiring521 is short-circuited with at least one of the other wirings. Thethreshold value I1 is determined in the similar manner as in the thirdembodiment.

The threshold value I2 is selected from a range larger than a possiblemaximal value of the photoelectric current and smaller than a possibleminimal value of the short-circuit current in order to distinguish thephotoelectric current from the short circuit current without fail. Themaximal value of the photoelectric current may be estimatedtheoretically from the multiplication of an intensity of ultravioletlaser light beam L by a surface area of the pad portion 412 a irradiatedby the light. The minimal value of the short circuit current istheoretically estimated from the multiplication of a dimension of ashort-circuited portion of the wirings by an applied voltage, with thedimension of the short-circuited portion being inferred from the designand production of the circuit board under test.

In this way, when an open/short circuit test of a wiring is completed,the routine returns to Step U711, and the aforementioned series ofoperations are implemented with respect to another wiring. Thus, theaforementioned series of operations are repeated until the test iscompleted with respect to all the wirings on the circuit board. Theother operations implemented by the apparatus in the second modificationare the same as those implemented by the apparatus shown in FIG. 17.

As mentioned above, the apparatus shown in FIG. 22 is operated to judgewhether the target wiring is in continuity based on a difference betweena photoelectric current I_(O) running in the case where the targetwiring is in a normal continuous state and a short circuit current I_(S)running in the case where the target wire is in a short circuit statewith the other wiring. This arrangement enables an open circuit test ofthe target wiring and a short circuit test of the target wiring relativeto the other wiring simultaneously.

In the apparatus shown in FIG. 22, in the case where the target wiringhas an open circuit portion x and a short circuit portion y at the sametime, the current value detected by the current detecting section 480 isabout the level of a short circuit current I_(S). Therefore, thecontroller 430 may prioritize the judgment that there is a short circuitportion in the target wiring, and resultantly misjudge that there is noopen circuit portion. Further, if the short circuit current I_(S) isabout the same level as that of the photoelectric current I_(O) due to alarge electric resistance at the short circuit portion, the controller430 may misjudge that the target wiring is in a normal continuous statedespite the fact that there is a short circuit portion.

In view of the above, a third modification of the third embodiment isproposed to solve the aforementioned drawback. FIG. 24 is a diagramshowing an apparatus as the third modification, and FIG. 25 is aflowchart showing operations of an open/short circuit test to beimplemented by the apparatus shown in FIG. 24. The apparatus of thethird modification enables detection of both open circuit and shortcircuit by implementing short circuit test after the test of continuityof a target in the manner as is done by the second modification of thethird embodiment. The arrangement of the third modification is identicalto that of the second modification except the following points. In thethird modification, a changeover switch 444 is additionally provided toswitch over the NC contacts of switch portions 443 of a multiplexer 442between the plus terminal and the minus terminal of a power source 460to render each switch portion 443 to be selectively connected to bothterminals or poles of the power source 460. Since the other arrangementof the third modification is identical to that of the secondmodification, elements of the third modification which are identical tothose of the second modification are denoted with the same referencenumerals, and a description thereof is omitted herein.

An open/short circuit test to be implemented by the apparatus of thethird modification is described with reference to FIGS. 24 and 25.First, at an initial stage of the test, the changeover switch 444 is setto a contact a with all the switches of multiplexer 442 being set to NCterminals to connect all the wirings on a circuit board 410 to the minusterminal of the power source 460 bypassing the a current detectingsection 480. Then, in Step U721, the multiplexer 442 is operated toselect one wiring 521 in response to a selection command from acontroller 430 to connect the wiring 521 to a current detecting section480. Upon lapse of a time until a fluctuation of current detection dueto a transient current becomes negligible (in Step U722), the currentdetecting section 480 measures a current running therethrough (in StepU723). Then, the controller 430 judges whether the wiring 521 is in anopen circuit state or not based on the measured current value.

Subsequently, the changeover switch 444 is switched over to a contact b,and a plus potential is applied to wirings 522 and 523 which are thewirings other than the target wiring 521 selected for the testing (inStep U725). Thereafter, upon lapse of a time (in Step U726), the currentdetecting section 480 measures a current running therethrough insubstantially the same manner as that of the open/short circuit testimplemented by the apparatus shown in FIG. 22, (in Step U727). Similarto the apparatus shown in FIG. 22, the controller 430 judges whetherthere is a short circuited portion between the wiring 521 and the otherwirings, based on the measured current value. Thus, upon completion ofthe open circuit test with respect to the wiring 521 and the shortcircuit test between the wiring 521 and the other wirings, thechangeover switch 444 is switched over to the contact a again (in StepU729). The aforementioned series of operations are repeated until theopen/short circuit test is completed with respect to all the wirings onthe circuit board 410 (in Step U739).

As mentioned above, the apparatus shown in FIG. 24 is arranged toperform an open circuit test and then a short circuit test by utilizingphotoelectric effect. This arrangement enables to perform an opencircuit test with respect to a target wiring and a short circuit testbetween the target wiring and the other wirings without the drawbacksthat an open circuit portion is neglected due to the presence of ashort-circuited portion and that an erroneous judgment that the targetwiring is in a normal continuous state is made despite the fact thatthere is a short-circuited portion in the target wiring.

In the third embodiments, the ultraviolet laser light is not necessaryin the short circuit test. In view of this, the arrangement of the thirdmodification may be so configured as to turn off the UV lamp 470 afterthe open circuit test. However, it is preferable to stabilize theintensity of ultraviolet laser light beam in order to perform a precisetest. To this end, it is practically desirable to keep turning the UVlamp 470 on until the open circuit test is completed with respect to allthe wirings formed on at least one work 410.

In the third modification, the changeover switch 444 is provided toselectively connect both terminals of the power source to the wiringsother than the target wiring. Another arrangement is available toselectively connect both terminals of the power source to the wiringsother than the target wiring. For instance, it may be possible toprovide an additional contact for each switch portion 443 of themultiplexer 442 in the apparatus shown in FIG. 22, connecting theadditional contact to the minus terminal of the power source 460.Switching over of the switch portions 443 enables selective switch overof the voltages applied to the other wirings while selecting the targetwiring.

FIG. 26 is a diagram showing a fourth modification of the thirdembodiment. The basic principle of the testing according to the fourthmodification is the same as the third embodiment except the manner ofapplying a voltage from a power source and the manner of collecting orcapturing the electrons discharged by the photoelectric effect.Accordingly, elements of the fourth modification that are identical tothose of the third embodiment are denoted at the same referencenumerals, and the fourth modification is described primarily focusing ondifferences between the fourth modification and the third embodiment.

The testing apparatus as the fourth modification is not provided with anelectrode on the housing 451 for trapping or capturing photoelectronsand is so configured as to trap or capture electrons discharged from atarget wiring, by applying a voltage to all or part of wirings formedaround the target wiring. To this end, in the fourth modification, theplus terminal of a power source 460 is connected to each NC contact ofeach switch portion 443 of a multiplexer 442, and the minus terminalthereof is connected to each NO contact of each switch portion 443 ofthe multiplexer 442 via a current detecting section 480.

Here, described is a case where, as shown in FIG. 26, a switch portion443 a connected to a wiring 521 of the multiplexer 442 is connected tothe NO contact to make the wiring 521 a target wiring to be tested. Inthis case, if the wiring 521 is in a normal continuous state, anelectric field is generated between pad portions 412 a of the wiringsother than the target wiring 521, and a pad portion 521 a of the targetwiring 521 when a voltage is applied between the target wiring 521 andthe other wirings. Electrons discharged from the pad portion 521 a ofthe target wiring 521 due to photoelectric effect by irradiation ofultraviolet laser light beam are electrically attracted by the padportion 512 a aided by the existence of the electric field or potential.In the above state, if the target wiring 521 is in continuity, aconductive circuit pathway is established through which a current runsfrom the power source 460 and returns thereto via the other wirings andthe target wiring 521. Thus, a current running through the target wiring521 is measured by the current detecting section 480.

On the other hand, if the target wiring 521 is not in continuity i.e.open circuited, the aforementioned conductive pathway is notestablished, and a current value detected by the current detectingsection 480 is zero or exceedingly lower than a current value detectedin the case where the wiring 521 is in continuity.

As mentioned above, the testing apparatus shown in FIG. 26 performs anopen circuit test of wirings in the similar manner as that of theapparatus shown in FIG. 17. In the fourth modification, it is notrequired to provide an electrode inside a housing 451. Therefore, thehousing 451 may be configured to have such a dimension as to cover awiring terminal or pad espousing area ER on a work 410 and to enclose aminimal space above the area ER. This arrangement enables a compact sizeof the apparatus while simplifying the construction of the apparatus.Further, since the volume of a closed space SP defined by the housing451, seal member 452, and the work 410 is reduced, a time required fordepressurizing the interior of the closed space SP is shortened with theresult that a test by the apparatus can be implemented in a short time.

In the fourth modification, it is required to perform a short circuittest between ball grid portions prior to an open circuit test. This isbecause if there is a short-circuited portion between the ball gridportions, a short circuit current may run through the current detectingsection 480 and the current detecting section 480 may make a misjudgmentthat there is no open circuit portion in the target wiring.

In the fourth modification, it is preferable to use a plurality ofwirings formed around a target wiring as the wirings serving as anelectrode. This is because if a single wiring is used as the electrode,and the wiring has an open circuit portion, accurate test cannot beperformed with such a testing apparatus.

In the fourth modification, it is possible to reverse the polarities ofthe power source 460 and to perform an open circuit test with respect toa target wiring by setting the target wiring at a high potential andsetting the other wirings serving as an electrode at a low potential.Specifically, in this altered case, an electric field having a directionof electron flow which is opposite to that of the fourth modification isgenerated between the pad portions 421 a of the other wirings and thepad portion 521 a of the target wiring 521. In this altered case, ifthere is an open circuit portion in the target wiring 521, theaforementioned conductive pathway is not established, and accordingly,the open circuit test with respect to the target wiring 521 can beperformed in the similar manner as the fourth modification.

This invention is not limited to the aforementioned embodiments andmodifications. Various modifications and alterations can be provided.For instance, in the third embodiment and its modifications, the circuitboard 410 to be tested as a work is of the type on which a semiconductorchip is mounted by C4 package method. Alternatively, this invention isapplicable to test a circuit board in which one surface of a base plateis formed with wirings or a circuit board formed with a cuffed wiringpattern.

In the third embodiment and its modifications, as described is the casewhere the interior of the housing is depressurized. Alternatively, adepressurization may not be required or the vacuum degree may be variedaccording to needs. This application is based on patent application Nos.2001-42356, 2001-111132, and 2001-111133 filed in Japan, the contents ofwhich are hereby incorporated by reference.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such change andmodifications depart from the scope or spirit of the invention, theyshould be construed as being included therein.

What is claimed is:
 1. A circuit board testing apparatus for testing aplurality of wirings formed on a circuit board, each wiring having afirst terminal and second terminal at opposite ends of each of thewirings, the apparatus comprising: an electromagnetic wave irradiatorwhich irradiates an electromagnetic wave onto a first terminal of aselected one of the wirings to discharge electrons from the irradiatedterminal by photoelectric effect; an electrode disposed at such aposition as to trap discharged electrons; a voltage supplier operativelyconnected between the electrode and the second terminal of the selectedwiring to apply voltage therebetween so that the electrode has a higherpotential than the second terminal of the selected wiring, the voltagesupplier including a probe operatively connected to the voltage supplierand connectable to the second terminal of the selected wiring; a currentdetector which detects an electric current that passes through theelectrode, the probe and the second terminal of the selected wiring; anda judger which determines existence of an open-circuit in the selectedwiring based on the current detected by the current detector.
 2. Thecircuit board testing apparatus according to claim 1, wherein theelectromagnetic wave irradiator includes a deflector which changes thedirection of the electromagnetic wave in such a manner as to selectivelyand successively irradiate the first terminals of the plurality ofwirings with the electromagnetic wave.
 3. The circuit board testingapparatus according to claim 1, wherein the voltage supplier includes apower source, and wherein the probe is a connector which electricallyconnects the power source, the electrode, the second terminal of theselected wiring, and the current detector with one another to therebyconstitute a closed circuit including a space between the electrode andthe first terminal of the selected wiring through which the dischargedelectrons flow.
 4. The circuit board testing apparatus according toclaim 3, wherein the connector includes a plurality of probes which areto be brought into contact with the respective second terminals of theplurality of wirings to establish electrical connections therewith, anda switch which selectively connects one of the plurality of probes tothe power source.
 5. The circuit board testing apparatus according toclaim 1, further comprising a housing which encloses the first terminalsof the plurality of wirings to constitute an airtight closed space, anda depressurizer which depressurizes the airtight closed space.
 6. Thecircuit board testing apparatus according to claim 5, wherein the upperportion of the housing is transparent, the electric magnetic waveirradiator is located above the housing to irradiate the first terminalsthrough the upper portion of the housing, and the electrode is formed onthe housing.
 7. The circuit board testing apparatus according to claim6, wherein the electrode includes a transparent electrode formed on anupper portion of the housing.
 8. The circuit board testing apparatusaccording to claim 6, wherein the electrode portion includes a meshedelectrode formed on the upper portion of the housing, and theelectromagnetic wave irradiator irradiates the first terminal throughthe upper portion of the housing not covered by the meshed electrode. 9.The circuit board testing apparatus according to claim 6, wherein theside wall of the housing is made of electrically conductive material andis electrically connected to the voltage supplier so as to be appliedwith the higher potential and function as the electrode to trap thedischarged electrons.
 10. The circuit board testing apparatus accordingto claim 1, wherein the voltage supplier includes a power source havinga plus terminal and a minus terminal, and a connector which connects theselected wiring to the minus terminal of the power source, and at leasta part of the unselected wirings to the the plus terminal of the powersource so that the wirings connected with the plus terminal of the powersource serve as the electrode to trap the discharged electrons.
 11. Thecircuit board testing apparatus according to claim 1, wherein thevoltage supplier includes a power source having a plus terminal and aminus terminal, and a switch arrangement which connects the selectedwiring to the minus terminal of the power source, and all unselectedwirings to the plus terminal of the power source so that the wiringsconnected with the plus terminal of the power source serve as theelectrode to trap the discharged electrons.
 12. The circuit boardtesting apparatus according to claim 1, wherein the voltage supplierincludes a power source, and a switch which connects the second terminalof the selected wiring to the power source.
 13. A circuit board testingapparatus for testing continuity and/or a short-circuit in wiringsformed on a circuit board, each wiring having first and second terminalsat opposite ends of the wiring, the apparatus comprising: anelectromagnetic wave irradiator which irradiates the first terminals ofthe wirings with an electromagnetic wave to allow electrons to bedischarged from the first terminals by photoelectric effect; anelectrode arranged to trap discharged electrons; a voltage supplierincluding a probe operatively connected to the voltage supplier andconnectable to at least one of the second terminals of the wirings, thevoltage supplier being operatively connected between the electrode andthe at least one of the second terminals to apply voltage therebetweenso that the electrode has a higher potential than the at least one ofthe second terminals; a current detector which detects an electriccurrent that passes through the electrode, the probe and the at leastone of the second terminals; and a judger which determines existence ofan open-circuit and/or a short-circuit in at least one of the wiringsbased on the current detected by the current detector.
 14. The circuitboard testing apparatus according to claim 13, wherein theelectromagnetic wave irradiator is arranged to alternatively irradiatethe terminals one at a time, and the voltage supplier is to bealternatively connected with the second terminals of the wirings one ata time.
 15. A circuit board testing apparatus for testing a plurality ofwirings formed on a circuit board, each wiring having a first and secondterminals at opposite ends of the wiring and the first terminals of thewirings being exposed on one surface of the circuit board, comprising:an electromagnetic wave irradiator which collectively irradiates thefirst terminals of the wirings with electromagnetic wave to dischargeelectrons from the first terminals by photoelectric effect; an electrodearranged to trap discharged electrons; a selector for selecting one ofthe wirings; a voltage supplier including a probe operatively connectedto the voltage supplier and connectable to at least one of the secondterminals of the wirings, the voltage supplier operatively connectedbetween the electrode and the at least one of the second terminals toapply voltage therebetween so that the electrode has a higher potentialthan the at least one of the second terminals; a current detector whichdetects an electric current that passes through the electrode, theprobe, and the at least one of the second terminals; and a judger whichjudges continuity and/or a short-circuit in at least one of the wiringsbased on the electric current detected by the current detector.
 16. Thecircuit board testing apparatus according to claim 15, wherein thevoltage supplier includes a power source having a plus pole connected tothe electrode and a minus pole connected to the second terminal of theselected wiring, and the selector includes a switch arrangement forelectrically connects the second terminals of the wirings other than theselected wiring, to the plus pole of the power source.
 17. The circuitboard testing apparatus according to claim 15, wherein the voltagesupplier includes a power source having a plus pole connected to theelectrode and a minus pole connected to the second terminal of theselected wiring, and the selector has a switch arrangement forelectrically connecting the second terminal of the selected wiring tothe minus pole of the power source by way of the current detector, andthe respective second terminals of the wirings other than the selectedwiring to the minus pole of the power source bypassing the currentdetector.
 18. The circuit board testing apparatus according to claim 17,wherein the selector includes a switch to select one state where thesecond terminal of the selected wiring is electrically connected to theminus pole of the power source by way of the current detector and thesecond terminals of the wirings other than the selected wiring areelectrically connected to the minus pole of the power source bypassingthe current detector, and another state where the second terminal of theselected wiring is electrically connected to the minus pole of the powersource by way of the current detector and the second terminals of thewiring other than the selected wiring are electrically connected to theplus pole of the power source.
 19. The circuit board testing apparatusaccording to claim 15, further comprising a housing which encloses thesecond terminals of the plurality of wirings to form an airtight closedspace, and a depressurizer which depressurizes the airtight closedspace.
 20. The circuit board testing apparatus according to claim 19,wherein the upper wall of the housing is transparent, theelectromagnetic wave irradiator is located above the housing toirradiate the first terminals through the transparent wall, and theelectrode is formed on the housing in the manner allowing the passage ofthe electromagnetic wave through the transparent wall.
 21. A method fortesting continuity and/or a short-circuit in at least one wiring formedon a circuit board, each wiring having first and second terminals, themethod comprising the steps of: providing an electrode operativelyconnected to a probe which is selectively connectable to at least one ofthe second terminals; irradiating at least one of the first terminals ofthe wirings with an electromagnetic wave to discharge electrons from theat least one of the first terminals into a space by photoelectriceffect; trapping discharged electrons by the electrode having apotential higher than at least one of the second terminals of thewirings and allowing a current caused by trapped electrons to flowthrough the electrode, the probe and the at least one of the secondterminals; detecting the current that flows through the electrode, theprobe and the at least one of the second terminals; and judgingcontinuity and/or a short-circuit in at least one of the wirings basedon the current flowing through the wiring.
 22. The method according toclaim 21, further comprising the following steps which are carried outprior to said step of irradiating: enclosing the space into whichelectrons are discharged; and depressurizing the space.
 23. The methodaccording to claim 21, wherein said step of irradiating includesselectively and successively irradiating the first terminals of thewirings one by one, and an electrical potential difference is producedbetween the electrode and the respective second terminal of the wiringbeing irradiated in such a manner that the electrode has a potentialhigher than that of the respective second terminal.
 24. The methodaccording to claim 21, wherein said step of irradiating includesselectively and successively irradiating the first terminals of thewirings one by one, and a difference of electric potential is producedbetween the electrode and a second terminal of a wiring adjacent to thewiring being irradiated in such a manner that the electrode has apotential higher than that of the second terminal of the wiring adjacentto the wiring being irradiated.
 25. The method according to claim 21,wherein said step of irradiating includes selectively and successivelyirradiating the first terminals of the wirings, and a difference ofelectric potential is produced between the electrode and the at leastone of the second terminals or between the electrode and at least one ofthe second terminals of the wirings adjacent to the wiring beingirradiated in such a manner that the electrode has a potential higherthan that of the at least one of the second terminals.
 26. A circuitboard testing apparatus for testing a plurality of wirings formed on acircuit board, each wiring having a first terminal and second terminalat opposite ends of each of the wirings, the apparatus comprising: anelectromagnetic wave irradiator which irradiates an electromagnetic waveonto a first terminal of a first selected wiring to discharge electronsfrom the irradiated terminal by photoelectric effect; an electrodedisposed at such a position as to trap discharged electrons; a voltagesupplier operatively connected between the electrode and a secondterminal of a second selected wiring to apply voltage therebetween sothat the electrode has a higher potential than the second terminal ofthe second selected wiring, the voltage supplier including a probeoperatively connected to the voltage supplier and connectable to thesecond terminal of the second selected wiring; a current detector whichdetects an electric current that passes through the electrode, the probeand the second terminal of the second selected wiring; and a judgerwhich determines existence of a short-circuit in the first selectedwiring based on the current detected by the current detector.
 27. Thecircuit board testing apparatus according to claim 26, wherein theelectromagnetic wave irradiator includes a deflector which changes thedirection of the electromagnetic wave in such a manner as to selectivelyand successively irradiate the first terminals of the plurality ofwirings with the electromagnetic wave.
 28. The circuit board testingapparatus according to claim 26, wherein the voltage supplier includes apower source, and wherein the probe is a connector which electricallyconnects the power source, the electrode, the second terminal of thesecond selected wiring, and the current detector with one another tothereby constitute a closed circuit including a space between theelectrode and the first terminal of the selected wiring through whichthe discharged electrons flow.
 29. The circuit board testing apparatusaccording to claim 28, wherein the connector includes a plurality ofprobes which are to be brought into contact with the respective secondterminals of the plurality of wirings to establish electricalconnections therewith, and a switch which selectively connects one ofthe plurality of probes to the power source.
 30. The circuit boardtesting apparatus according to claim 26, further comprising a housingwhich encloses the first terminals of the plurality of wirings toconstitute an airtight closed space, and a depressurizer whichdepressurizes the airtight closed space.
 31. The circuit board testingapparatus according to claim 30, wherein the upper portion of thehousing is transparent, the electric magnetic wave irradiator is locatedabove the housing to irradiate the first terminals through the upperportion of the housing, and the electrode is formed on the housing. 32.The circuit board testing apparatus according to claim 31, wherein theelectrode includes a transparent electrode formed on an upper portion ofthe housing.
 33. The circuit board testing apparatus according to claim31, wherein the electrode portion includes a meshed electrode formed onthe upper portion of the housing, and the electromagnetic waveirradiator irradiates the first terminal through the upper portion ofthe housing not covered by the meshed electrode.
 34. The circuit boardtesting apparatus according to claim 31, wherein the side wall of thehousing is made of electrically conductive material and is electricallyconnected to the voltage supplier so as to be applied with the higherpotential and function as the electrode to trap the dischargedelectrons.
 35. The circuit board testing apparatus according to claim26, wherein the voltage supplier includes a power source having a plusterminal and a minus terminal, and a connector which connects the firstselected wiring to the minus terminal of the power source, and at leasta part of the unselected wirings to the plus terminal of the powersource so that the wirings connected with the plus terminal of the powersource serve as the electrode to trap the discharged electrons.
 36. Thecircuit board testing apparatus according to claim 26, wherein thevoltage supplier includes a power source having a plus terminal and aminus terminal, and a switch arrangement which connects the firstselected wiring to the minus terminal of the power source, and allunselected wirings to the plus terminal of the power source sp that thewirings connected with the plus terminal of the power source serve asthe electrode to trap the discharged electrons.
 37. The circuit boardtesting apparatus according to claim 26, wherein the voltage supplierincludes a power source, and a switch which connects the power source tothe second terminal of the second selected wiring, and wherein thesecond selected wiring is adjacent to the first selected wiring.